internal/gcimporter: renable tests of issue50259.go

Now that the compiler support for gotypesalias=1 is
fixed (by CL 574737), we can reenable these tests.

Updates golang/go#66550
Updates golang/go#65294

Change-Id: I70b187c561d2eeb3f7a4cc078107b7bcce5ced01
Reviewed-on: https://go-review.googlesource.com/c/tools/+/576139
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Tim King <taking@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>

internal/gcimporter/gcimporter_test.go

@@ -190,7 +190,6 @@ func TestImportTypeparamTests(t *testing.T) {
 			"nested.go":     "fails to compile",              // TODO(rfindley): investigate this.
 			"issue47631.go": "can not handle local type declarations",
 			"issue55101.go": "fails to compile",
-			"issue50259.go": "compiler crashes if GODEBUG=gotypesalias=1", // TODO(adonovan): delete when #66550 is fixed.
 		}
 	}
 

internal/gcimporter/iexport_go118_test.go

@@ -123,12 +123,6 @@ func TestImportTypeparamTests(t *testing.T) {
 				t.Fatal(err)
 			}
 
-			// TODO(adonovan): delete when #66550 is fixed.
-			if strings.Contains(os.Getenv("GODEBUG"), "gotypesalias=1") &&
-				entry.Name() == "issue50259.go" {
-				t.Skip("Skipping test of defined<->alias cycle under gotypesaliases=1 (#66550)")
-			}
-
 			if !bytes.HasPrefix(src, []byte("// run")) && !bytes.HasPrefix(src, []byte("// compile")) {
 				// We're bypassing the logic of run.go here, so be conservative about
 				// the files we consider in an attempt to make this test more robust to