revert: drop now useless conditional in the backup check

Now that we removed the (hopeless) attempt to backup file we knew to be
missing in the target changeset, we can stop checking if the file exists in
the target changeset.

mercurial/cmdutil.py

@@ -2551,8 +2551,8 b' def revert(ui, repo, ctx, parents, *pats'
                     continue
                 if xlist is not None:
                     xlist.append(abs)
-                    if (dobackup and os.path.lexists(target) and
-                        abs in ctx and repo[None][abs].cmp(ctx[abs])):
+                    if (dobackup and os.path.lexists(target)
+                        and repo[None][abs].cmp(ctx[abs])):
                         bakname = "%s.orig" % rel
                         ui.note(_('saving current version of %s as %s\n') %
                                 (rel, bakname))