cmd/compile/internal/types2: use go/types/testdata/spec tests

Since the spec tests are now identical between the two type checkers,
remove the local copy of the spec tests and (for now) use the tests
in go/types/testdata/spec instead. Eventually we may decide to move
all tests out of the type checker directories and place them in a
shared space (e.g. internal/types/testdata).

For #54511.

Change-Id: Ibc62230553a5ff215160dcc97696b333ae9cf685
Reviewed-on: https://go-review.googlesource.com/c/go/+/424676
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>

src/cmd/compile/internal/types2/check_test.go

@@ -298,7 +298,7 @@ func TestManual(t *testing.T) {
 // TODO(gri) go/types has extra TestLongConstants and TestIndexRepresentability tests
 
 func TestCheck(t *testing.T)     { DefPredeclaredTestFuncs(); testDirFiles(t, "testdata/check", 55, false) } // TODO(gri) narrow column tolerance
-func TestSpec(t *testing.T)      { testDirFiles(t, "testdata/spec", 0, false) }
+func TestSpec(t *testing.T)      { testDirFiles(t, "../../../../go/types/testdata/spec", 0, false) }
 func TestExamples(t *testing.T)  { testDirFiles(t, "testdata/examples", 45, false) }
 func TestFixedbugs(t *testing.T) { testDirFiles(t, "testdata/fixedbugs", 0, false) }