Revert "subversion: make python bindings build on 10.9."

Based on feedback from the subversion issue tracker, will backport r1535610
instead.

This reverts commit 06031e61e3fd2ebbbb76f1a8ed4e539d4e5a8fac.
subversion: make perl/ruby/python bindings build.

Need to filter out CPPFLAGS that confuse swig, see #23993.