audio/libcanberra: split a gtk2 from non graphic port

there was already a slave port for gtk3, now make a slaveport for gtk2 as
well.

While here fix the option definition which was wrongly done making libcanberra
have no options at all while libcanberra-gtk3 had and the opposite was expected

Use options helpers to simplify the port.
Drop the gtkdoc by default
bump revision and track no package for the 2 only port requiring the gtk2 library
Reduce the slave port to its bare minimal requirement

This change has been made in a slaveport instead of a flavor, because flavors depending
on its own origin is not supported. this is a candidate for subpackages in the futur.

note that this changes also removes gtk2 from the dependency path of many gtk3 only
application