release.py: Use subversion.asc instead of subversion-pmc.asc for get-keys.

All Subversion committers can sign releases not just PMC members.

* tools/dist/release.py:
  (KEYS): Use subversion.asc instead of subversion-pmc.asc.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1428213 13f79535-47bb-0310-9956-ffa450edef68