vfs: use 'vfs' module directly in 'test-lock'

Now that the 'vfs' classes moved in their own module, lets use the new module
directly. We update code iteratively to help with possible bisect needs in the
future.

tests/test-lock.py

@@ -10,7 +10,7 b' import unittest'
 from mercurial import (
     error,
     lock,
-    scmutil,
+    vfs as vfsmod,
 )
 
 testlockname = 'testlock'
@@ -36,7 +36,7 b' class teststate(object):'
         self._acquirecalled = False
         self._releasecalled = False
         self._postreleasecalled = False
-        self.vfs = scmutil.vfs(dir, audit=False)
+        self.vfs = vfsmod.vfs(dir, audit=False)
         self._pidoffset = pidoffset
 
     def makelock(self, *args, **kwargs):