[release-branch.go1.19] cmd/go: remove tests that assume lack of new versions of external modules

In general it seems ok to assume that an open-source module that did
exist will continue to do so — after all, users of open-source modules
already do that all the time. However, we should not assume that those
modules do not publish new versions — that's really up to their
maintainers to decide.

Two existing tests did make that assumption for the module
gopkg.in/natefinch/lumberjack.v2. Let's remove those two tests.
If we need to replace them at some point, we can replace them with
hermetic test-only modules (#54503) or perhaps modules owned by the Go
project.

Updates #58445.
Fixes #58449.

Change-Id: Ica8fe587d86fc41f3d8445a4cd2b8820455ae45f
Reviewed-on: https://go-review.googlesource.com/c/go/+/466862
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

Author: Bryan C. Mills

src/cmd/go/internal/modfetch/coderepo_test.go

@@ -378,18 +378,6 @@ var codeRepoTests = []codeRepoTest{
 		zipSum:      "h1:YJYZRsM9BHFTlVr8YADjT0cJH8uFIDtoc5NLiVqZEx8=",
 		zipFileHash: "c15e49d58b7a4c37966cbe5bc01a0330cd5f2927e990e1839bda1d407766d9c5",
 	},
-	{
-		vcs:         "git",
-		path:        "gopkg.in/natefinch/lumberjack.v2",
-		rev:         "latest",
-		version:     "v2.0.0-20170531160350-a96e63847dc3",
-		name:        "a96e63847dc3c67d17befa69c303767e2f84e54f",
-		short:       "a96e63847dc3",
-		time:        time.Date(2017, 5, 31, 16, 3, 50, 0, time.UTC),
-		gomod:       "module gopkg.in/natefinch/lumberjack.v2\n",
-		zipSum:      "h1:AFxeG48hTWHhDTQDk/m2gorfVHUEa9vo3tp3D7TzwjI=",
-		zipFileHash: "b5de0da7bbbec76709eef1ac71b6c9ff423b9fbf3bb97b56743450d4937b06d5",
-	},
 	{
 		vcs:  "git",
 		path: "gopkg.in/natefinch/lumberjack.v2",
@@ -792,11 +780,6 @@ var codeRepoVersionsTests = []struct {
 		path:     "swtch.com/testmod",
 		versions: []string{"v1.0.0", "v1.1.1"},
 	},
-	{
-		vcs:      "git",
-		path:     "gopkg.in/natefinch/lumberjack.v2",
-		versions: []string{"v2.0.0"},
-	},
 	{
 		vcs:      "git",
 		path:     "vcs-test.golang.org/git/odd-tags.git",