Follow-up to r1508225: don't include svn_private_config.h in
mod_dav_svn as this leads to duplicate package definitions.

* subversion/mod_dav_svn/activity.c,
  subversion/mod_dav_svn/deadprops.c,
  subversion/mod_dav_svn/lock.c,
  subversion/mod_dav_svn/merge.c,
  subversion/mod_dav_svn/mod_dav_svn.c,
  subversion/mod_dav_svn/reports/update.c,
  subversion/mod_dav_svn/repos.c,
  subversion/mod_dav_svn/version.c: remove #include svn_private_config.h

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1508244 13f79535-47bb-0310-9956-ffa450edef68