video: fix up GstVideoOrientationMethod type registration

video: fix up GstVideoOrientationMethod type registration

... in order to make older g-i happy (~1.60) which doesn't like
freeform descriptions in the value_name field. Which in turn
then makes hotdoc happy instead of erroring out when we bump
the symbol index version.

We usually only (ab)use the name field for description strings
for private plugin enums, not for public API visible to bindings.

This lets glib-mkenum generate the _get_type() function for the
enum again, which in turn will generate the expected value names
to match the enums.

We might be able to add this back later once we can upgrade the
g-i version requirement (and the documentation job image).

This reverts most of commit b0aab48cdcf0a454d14aeb4d907209d8ee3f1add