gst1-validate: bump version to 1.12.0

Remove non-existant configure options:

  --disable-sphinx-doc:
  Even if it looks like there is some code for that in configure.ac, it
  seems that is not taken into account and that configure option is not
  even recognized.

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>