go/types: include test/fixedbugs/bug073.go again in test

This test was excluded from the go/types std lib test
because it tested old behavior (shift count must be
an unsigned int). With the compiler changes made and
the test adjusted accordingly, we can include it again.

Updates #19113.

Change-Id: If9b6b83505d2bd2b426fcefa225986d73658a229
Reviewed-on: https://go-review.googlesource.com/c/159319Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

src/go/types/stdlib_test.go

@@ -167,7 +167,6 @@ func TestStdFixed(t *testing.T) {
 	}
 
 	testTestDir(t, filepath.Join(runtime.GOROOT(), "test", "fixedbugs"),
-		"bug073.go",                           // checks for unsigned integer shift - disabled for now
 		"bug248.go", "bug302.go", "bug369.go", // complex test instructions - ignore
 		"issue6889.go",   // gc-specific test
 		"issue7746.go",   // large constants - consumes too much memory