Tip introduces a new internal/poll package that breaks the expected
output.

Fixes golang/go#19150
Updates golang/go#19152

Change-Id: I5ff7e8a92afe4d25feb6365933062e931c9b435f
Reviewed-on: https://go-review.googlesource.com/37148
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

The check was there to test that the loader worked with a cycle between the
three augmented packages compress/bzip2, io/ioutil, and regexp, because of
dependencies between each of the packages' tests and the next package.

The test in io/ioutil that had the dependency that created the cycle no longer
exists in that package (it's been moved out into the ioutil_test xtest).
Remove the check for that package.

Unfortunately this means that the cycle that was being checked for before is no
longer being checked. That could be fixed in a future change by creating three
fake packages in testdata that have this relationship.

Fixes golang/go#38318
Updates golang/go#19152

Change-Id: I8ce88102a5505d8edf8d54d2098c85a8d3cd622f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/227772
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>