freeswitch-stable: upgrade to 1.8.1

freeswitch-stable: upgrade to 1.8.1

- Bump version from 1.6.20 to 1.8.1 (includes OpenSSL 1.1.0 support).
- Upstream didn't provide a source tarball yet, switch to git to grab
  the release.
- freeradius-client got updated to 1.1.7 by upstream, update version and
  checksum accordingly.
- tiff, libvpx and pcre patches are no longer needed, drop them.
- Refresh the remaining patches. Only minor changes were needed.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>