Remove useless import (since 669009c3672c)

Note: this import is no more valid since hg 1ac628cd7113

mercurial_keyring.py

@@ -23,7 +23,6 b' try:'
     from mercurial.url import passwordmgr
 except:
     from mercurial.httprepo import passwordmgr
-from mercurial.httprepo import httprepository
 from mercurial import mail
 from urllib2 import AbstractBasicAuthHandler, AbstractDigestAuthHandler