Auto merge of #1636 - RalfJung:rustup, r=oli-obk

remove miri-rustc-tests

`@oli-obk` I am not sure if anyone used this program in the last few years. There are no instructions for how to use it. So I think keeping it working is just a waste of time. It now fails to build:
```
error[E0046]: not all trait items implemented, missing: `visit_foreign_item`
  --> src/bin/miri-rustc-tests.rs:36:17
   |
36 |                 impl<'tcx, 'hir> itemlikevisit::ItemLikeVisitor<'hir> for Visitor<'tcx> {
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `visit_foreign_item` in implementation
```
So I propose instead of me trying to figure out how to fix this, we just drop this ancient code.

Cargo.toml

@@ -17,12 +17,6 @@ name = "miri"
 test = false # we have no unit tests
 doctest = false # and no doc tests
 
-[[bin]]
-name = "miri-rustc-tests"
-test = false # we have no unit tests
-doctest = false # and no doc tests
-required-features = ["rustc_tests"]
-
 [dependencies]
 getrandom = { version = "0.2", features = ["std"] }
 env_logger = "0.7.1"
@@ -46,6 +40,3 @@ libc = "0.2"
 compiletest_rs = { version = "0.5", features = ["tmp"] }
 rustc_version = "0.2.3"
 colored = "2"
-
-[features]
-rustc_tests = []

rust-version

@@ -1 +1 @@
-828461b4b27c4a955587887936e54057efc5e2c1
+88b81970ba7a989a728b32039dd075dc206f1360