Reduce visibility of a function.

* subversion/svnserve/server.h
  (load_authz_config): Remove declaration.

* subversion/svnserve/serve.c
  (load_authz_config): Mark static.  Also move here the docstring from the
    now-removed declaration.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1511215 13f79535-47bb-0310-9956-ffa450edef68