go/types: reenable disabled test (backport from std repo go/types)

Change-Id: I93a914dcfc5bd2cfa8078cec683a46225b665e44
Reviewed-on: https://go-review.googlesource.com/8626
Reviewed-by: Alan Donovan <adonovan@google.com>

go/types/stdlib_test.go

@@ -119,7 +119,6 @@ func TestStdTest(t *testing.T) {
 	testTestDir(t, filepath.Join(runtime.GOROOT(), "test"),
 		"cmplxdivide.go", // also needs file cmplxdivide1.go - ignore
 		"sigchld.go",     // don't work on Windows; testTestDir should consult build tags
-		"float_lit2.go",  // TODO(gri) enable for releases 1.4 and higher
 	)
 }