tests: remove bundle2 activation from test-bookmark-pushpull.t

This is an old config that predate bundle2 on by default. This should have been
remove after Mercurail 3.6 got released.

tests/test-bookmarks-pushpull.t

@@ -7,9 +7,6 b''
   > publish=False
   > [experimental]
   > evolution=createmarkers,exchange
-  > # drop me once bundle2 is the default,
-  > # added to get test change early.
-  > bundle2-exp = True
   > EOF
 
 initialize