remove useless import of repo

This broke on Mercurial 2.3 when demandimport was not enabled

mercurial_keyring.py

@@ -17,7 +17,7 b' command line). This extension uses and w'
 library.
 '''
 
-from mercurial import hg, repo, util
+from mercurial import hg, util
 from mercurial.i18n import _
 try:
     from mercurial.url import passwordmgr