gopls/internal/regtest/misc: update some unilaterally skipped tests

Remove skips for two tests related to line directives (now fixed), and
delete a test related to the old parse cache, which no longer exists.

Updates golang/go#53878

Change-Id: I15b1e5d72f5ccc8c094eaa43e73a9bcc1f75c031
Reviewed-on: https://go-review.googlesource.com/c/tools/+/496882
Reviewed-by: Peter Weinberger <pjw@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>

Author: findleyr

gopls/internal/regtest/misc/failures_test.go

@@ -15,7 +15,6 @@ import (
 // that includes a line directive, which makes no difference since
 // gopls ignores line directives.
 func TestHoverFailure(t *testing.T) {
-	t.Skip("line directives //line ")
 	const mod = `
 -- go.mod --
 module mod.com
@@ -48,7 +47,6 @@ func main() {
 // This test demonstrates a case where gopls is not at all confused by
 // line directives, because it completely ignores them.
 func TestFailingDiagnosticClearingOnEdit(t *testing.T) {
-	t.Skip("line directives //line ")
 	// badPackageDup contains a duplicate definition of the 'a' const.
 	// This is a minor variant of TestDiagnosticClearingOnEdit from
 	// diagnostics_test.go, with a line directive, which makes no difference.