Following up on r1591919, adjust a couple of outdated comments.

No functional change.

* subversion/libsvn_fs_fs/fs.c
  (fs_serialized_init): All of our svn_mutex__t objects are now enabled by
    default, so the "enabled unconditionally" part of the comment is now
    unnecessary and can probably confuse the readers.

* subversion/libsvn_fs_x/fs.c
  (x_serialized_init): Same here.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1618226 13f79535-47bb-0310-9956-ffa450edef68