The flag processors test for duplicate processors for a single flag
was misleading because the file from the previous test case caused it
to fail (making the "echo 'this should fail' > file" part
irrelevant). Let's remove the leftover from the previous test case to
make it clear that duplicate flag processors results only in a
warning.
Note that duplicate flag processors would have resulted in a failure
(not just a warning) until ea1c2eb7abd3 (extensions: catch uisetup and
extsetup failures and don't let them break hg, 2017-06-06). I remember
expressing my concern about ending up with half-loaded extensions. It
would be pretty unfortunate to have double-encoded revlog content
enter a repo, so maybe we should reconsider?