Fix / silence a few integer conversion warnings in FSX.

* subversion/libsvn_fs_x/index.c
  (l2p_proto_index_lookup): Remove unnecessary cast.

* subversion/libsvn_fs_x/noderevs.c
  (svn_fs_x__read_noderevs_container): Cast to entry counts to APR index type.
                                       Since the size of the whole container
                                       is limited to a few MB, there is no way
                                       to have more than 2G entries in it.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1616598 13f79535-47bb-0310-9956-ffa450edef68