deskutils/caja-extensions: switch to GitHub release asset

Minor versions of 1.28.x are no longer published to the MATE mirror
and are only available on GitHub. Use USE_GITHUB=nodefault with a
release tarball instead of the auto-generated one, as recommended
by the porter's handbook. Remove autoreconf and gtkdocize, not needed
with release tarballs. Patch sendto/Makefile.in to skip installing
pre-built API docs.