test-revlog-raw: drop the overwrite of dead code

The revlog class no longer have a _isgooddeltainfo method for a long time. So
overwriting it does not get us anything. The test have been wrapping the right
code since then anyway.

tests/test-revlog-raw.py

@@ -54,10 +54,6 b' tvfs.options = {'
     b'sparse-revlog': True,
 }
 
-# The test wants to control whether to use delta explicitly, based on
-# "storedeltachains".
-revlog.revlog._isgooddeltainfo = lambda self, d, textlen: self._storedeltachains
-
 
 def abort(msg):
     print('abort: %s' % msg)