rollback: avoid a `hg commit --addremove` at a critical point

The rollback behavior around `hg commit --addremove` has changed slightly. It
does not really matters here but keeping that variant out of the way cannot
hurt.

tests/test-rollback.t

@@ -70,8 +70,8 b' working dir unaffected by rollback: do n'
   |
   o  0  [default] (bar) add a again
   
-  $ hg commit -Am'add b'
-  adding b
+  $ hg add b
+  $ hg commit -m'add b'
   $ hg log -G --template '{rev}  [{branch}] ({bookmarks}) {desc|firstline}\n'
   @  2  [test] (foo) add b
   |