rebase: inline simple function for finding obsolete subset of commits

`_filterobsoleterevs()` is just one line long. It was introduced in
2d294dada4f8 (rebase: small refactoring to allow better extensibility
from extensions, 2016-01-14), for use by the "inhibit" extension. That
extension was removed from the evolve repo in 87e87881059d (compat:
drop the inhibit hacky extension, 2017-10-24).

Differential Revision: https://phab.mercurial-scm.org/D10198

hgext/rebase.py

@@ -474,7 +474,7 b' class rebaseruntime(object):'
                         )
 
         # Calculate self.obsoletenotrebased
-        obsrevs = _filterobsoleterevs(self.repo, self.state)
+        obsrevs = {r for r in self.state if self.repo[r].obsolete()}
         self._handleskippingobsolete(obsrevs, self.destmap)
 
         # Keep track of the active bookmarks in order to reset them later
@@ -2184,11 +2184,6 b' def pullrebase(orig, ui, repo, *args, **'
     return ret
 
 
-def _filterobsoleterevs(repo, revs):
-    """returns a set of the obsolete revisions in revs"""
-    return {r for r in revs if repo[r].obsolete()}
-
-
 def _computeobsoletenotrebased(repo, rebaseobsrevs, destmap):
     """Return (obsoletenotrebased, obsoletewithoutsuccessorindestination).