rebase: delete obsolete internal "keepopen" option

The option was apparently introduced for use by the "pbranch"
extension, see f2558a8228be (rebase: add option to not commit after a
collapsing, 2010-02-07). However, it doesn't seem like it was ever
used by that extension (according to `hg grep` in a clone of
https://bitbucket.org/parren/hg-pbranch/), so let's delete it.

Differential Revision: https://phab.mercurial-scm.org/D2708

hgext/rebase.py

@@ -174,9 +174,6 b' class rebaseruntime(object):'
 
         self.keepf = opts.get('keep', False)
         self.keepbranchesf = opts.get('keepbranches', False)
-        # keepopen is not meant for use on the command line, but by
-        # other extensions
-        self.keepopen = opts.get('keepopen', False)
         self.obsoletenotrebased = {}
         self.obsoletewithoutsuccessorindestination = set()
         self.inmemory = inmemory
@@ -551,7 +548,7 b' class rebaseruntime(object):'
         repo, ui, opts = self.repo, self.ui, self.opts
         fm = ui.formatter('rebase', opts)
         fm.startitem()
-        if self.collapsef and not self.keepopen:
+        if self.collapsef:
             p1, p2, _base = defineparents(repo, min(self.state), self.destmap,
                                           self.state, self.skipped,
                                           self.obsoletenotrebased)