gst1-plugins-bad: update configure options

- add new onvif option
- add new dtls option
- add new openh264 option
- add new x265 option
- removed real plugin option
- add new rtp option
- remove always disabled legacy options: directdraw, osx_video,
  quicktime and mythtv
- add '--disable-bs2b' and '--disable-libde265' to options
  which require currently unpackaged libraries
- add '--disable-gtk3' and '--disable-qt'

[Thomas: improve wording of Config.in.legacy option.]

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>