mq: drop an unused variable assignment

Flagged by PyCharm.  This variable is the index of a `for` loop below.

Differential Revision: https://phab.mercurial-scm.org/D7755

hgext/mq.py

@@ -2256,7 +2256,6 b' class queue(object):'
     def restore(self, repo, rev, delete=None, qupdate=None):
         desc = repo[rev].description().strip()
         lines = desc.splitlines()
-        i = 0
         datastart = None
         series = []
         applied = []