tests/test-check-pyflakes.t

extensions: drop maxlength from enabled and disabled

This is a bad/silly API. Instead calculate maxlength in one place in help
it's used and simplify all the callers.

  $ "$TESTDIR/hghave" pyflakes || exit 80
  $ cd $(dirname $TESTDIR)
  $ pyflakes mercurial hgext 2>&1 | $TESTDIR/filterpyflakes.py
  mercurial/hgweb/server.py:*: 'activeCount' imported but unused (glob)
  mercurial/commands.py:*: 'base85' imported but unused (glob)
  mercurial/commands.py:*: 'bdiff' imported but unused (glob)
  mercurial/commands.py:*: 'mpatch' imported but unused (glob)
  mercurial/commands.py:*: 'osutil' imported but unused (glob)
  mercurial/revlog.py:*: 'short' imported but unused (glob)
  hgext/inotify/linux/__init__.py:*: 'from _inotify import *' used; unable to detect undefined names (glob)
  mercurial/util.py:*: 'from posix import *' used; unable to detect undefined names (glob)
  mercurial/windows.py:*: 'from win32 import *' used; unable to detect undefined names (glob)
  mercurial/util.py:*: 'from windows import *' used; unable to detect undefined names (glob)