package/gssdp: explicitly disable vapi

Currently, vapi support does not work with meson due to meson calling vapigen
directly instead of the vala wrapper. As such, when building typelib files for
gobject-introspection, vapigen fails to find the proper .gir files and fails
to build.

Explicitly disable vapi until a fix for vapi is made.

Signed-off-by: Adam Duskett <Aduskett@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>