Remove the last usage of simple_request_context_t.
Remove the last usage of simple_request_context_t.

* subversion/libsvn_ra_serf/locks.c:
  (svn_ra_serf__unlock): add a comment about future work. remove the
    CTX localvar. switch to expect_empty_body and run_one.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion