revset: drop an outdated comment

There is not `ui.expandpath` call there anymore.

Differential Revision: https://phab.mercurial-scm.org/D10435

mercurial/revset.py

@@ -1856,7 +1856,6 b' def outgoing(repo, subset, x):'
         l and getstring(l[0], _(b"outgoing requires a repository path")) or b''
     )
     if dest:
-        # ui.getpath() explicitly tests for None, not just a boolean
         dests = [dest]
     else:
         dests = []