amend: removing redundant if condition

There is needless checking for the new commit hash not being equal to
the old commit hash. This condition will always be true at this point in the
code path and thus, can be removed safely. This commit removes the redundant
condition.

Test Plan:
ran the test suite.

Differential Revision: https://phab.mercurial-scm.org/D594

mercurial/cmdutil.py

@@ -3173,13 +3173,14 b' def amend(ui, repo, commitfunc, old, ext'
             newid = repo.commitctx(new)
         finally:
             repo.ui.setconfig('phases', 'new-commit', ph, 'amend')
-        if newid != old.node():
+
             # Reroute the working copy parent to the new changeset
             repo.setparents(newid, nullid)
             mapping = {old.node(): (newid,)}
             if node:
                 mapping[node] = ()
             scmutil.cleanupnodes(repo, mapping, 'amend')
+
     return newid
 
 def commiteditor(repo, ctx, subs, editform=''):