fastannotate: address pyflakes concerns

Two unused imports, one unused local variable assignment.

Differential Revision: https://phab.mercurial-scm.org/D4337

hgext/fastannotate/__init__.py

@@ -117,7 +117,6 b' from mercurial import ('
     error as hgerror,
     localrepo,
     registrar,
-    util,
 )
 
 from . import (

hgext/fastannotate/protocol.py

@@ -15,7 +15,6 b' from mercurial import ('
     extensions,
     hg,
     localrepo,
-    scmutil,
     wireprotov1peer,
     wireprotov1server,
 )
@@ -188,8 +187,6 b' def _filterfetchpaths(repo, paths):'
     if threshold <= 0:
         return paths
 
-    master = repo.ui.config('fastannotate', 'mainbranch') or 'default'
-
     result = []
     for path in paths:
         try: