Add error tracing in two functions that try to remove a repository.

* subversion/libsvn_fs_fs/fs.c
  (fs_delete_fs): Add error tracing.

* subversion/libsvn_repos/repos.c
  (svn_repos_delete): Add error tracing.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1628161 13f79535-47bb-0310-9956-ffa450edef68