* tools/dev/unix-build/Makefile.svn: Use 'make clean-swig' to remove
   pre-generated swig files. Previously, the 'make extraclean-swig'
   target was used for this but that target was removed in r1301760.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1479319 13f79535-47bb-0310-9956-ffa450edef68