Only check for unused mut user variables and not all arguments

[KiChjang]

Fixes #50343.

[rust-highfive]

r? @pnkfelix

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[rust-highfive]

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:06:16] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:06:16] tidy error: /checkout/src/test/run-pass/nll/issue-50343.rs: missing trailing newline
[00:06:18] some tidy checks failed
[00:06:18] 
[00:06:18] 
[00:06:18] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:06:18] 
[00:06:18] 
[00:06:18] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:06:18] Build completed unsuccessfully in 0:02:20
[00:06:18] Build completed unsuccessfully in 0:02:20
[00:06:18] Makefile:79: recipe for target 'tidy' failed
[00:06:18] make: *** [tidy] Error 1

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:00d46020
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[rust-highfive]

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#insecureplatformwarning.
  InsecurePlatformWarning
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#insecureplatformwarning.
  InsecurePlatformWarning
  Downloading https://files.pythonhosted.org/packages/3f/6c/dbbd5992740649134e597833bea5a95e1fc093a7123e9b8156d838b960e4/awscli-1.15.11-py2.py3-none-any.whl (1.3MB)
    0% |▎                               | 10kB 11.5MB/s eta 0:00:01
    1% |▌                               | 20kB 1.9MB/s eta 0:00:01
    2% |▉                               | 30kB 2.2MB/s eta 0:00:01
    3% |█                               | 40kB 2.0MB/s eta 0:00:01
---
    100% |████████████████████████████████| 61kB 7.8MB/s 
Collecting botocore==1.10.11 (from awscli)
/usr/local/lib/python2.7/dist-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#insecureplatformwarning.
  InsecurePlatformWarning
  Downloading https://files.pythonhosted.org/packages/15/c0/04ec8aec3cdf7dd4887f2666044550eb3370a4f29668e53519cc7143bdcf/botocore-1.10.11-py2.py3-none-any.whl (4.2MB)
    0% |                                | 10kB 49.5MB/s eta 0:00:01
    0% |▏                               | 20kB 50.4MB/s eta 0:00:01
    0% |▎                               | 30kB 57.3MB/s eta 0:00:01
    0% |▎                               | 40kB 18.7MB/s eta 0:00:01
---
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--rustc-path" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "--src-base" "/checkout/src/test/compile-fail" "--build-base" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/compile-fail" "--stage-id" "stage2-x86_64-unknown-linux-gnu" "--mode" "compile-fail" "--target" "x86_64-unknown-linux-gnu" "--host" "x86_64-unknown-linux-gnu" "--llvm-filecheck" "/usr/lib/llvm-3.9/bin/FileCheck" "--host-rustcflags" "-Crpath -O -Zunstable-options " "--target-rustcflags" "-Crpath -O -Zunstable-options  -Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers" "--docck-python" "/usr/bin/python2.7" "--lldb-python" "/usr/bin/python2.7" "--gdb" "/usr/bin/gdb" "--quiet" "--llvm-version" "3.9.1\n" "--system-llvm" "--cc" "" "--cxx" "" "--cflags" "" "--llvm-components" "" "--llvm-cxxflags" "" "--adb-path" "adb" "--adb-test-dir" "/data/tmp/work" "--android-cross-path" "" "--color" "always"
[00:55:41] 
[00:55:41] 
[00:55:41] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test
[00:55:41] Build completed unsuccessfully in 0:16:17
[00:55:41] Build completed unsuccessfully in 0:16:17
[00:55:41] make: *** [check] Error 1
[00:55:41] Makefile:58: recipe for target 'check' failed

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:03f1f988
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[KiChjang]

@TimNN The logs above don't show the relevant error logs.

[KiChjang]

This looks like it's the wrong fix, closing.