narrow: remove hack to read narowspec from shared .hg directory

This was another leftover from 576eef1ab43d (narrow: move
.hg/narrowspec to .hg/store/narrowspec (BC), 2018-08-02), in addition
to 623081f2abc2 (narrow: remove hack to write narrowspec to shared .hg
directory, 2018-09-12).

Differential Revision: https://phab.mercurial-scm.org/D4692

mercurial/localrepo.py

@@ -1032,11 +1032,7 b' class localrepository(object):'
 
         A tuple of (includes, excludes).
         """
-        source = self
-        if self.shared():
-            from . import hg
-            source = hg.sharedreposource(self)
-        return narrowspec.load(source)
+        return narrowspec.load(self)
 
     @storecache(narrowspec.FILENAME)
     def _narrowmatch(self):