rtph263ppay: remove annex-? fields in caps if not present [pexhack]
rtph263ppay: remove annex-? fields in caps if not present [pexhack]

Change so that if the intersection of upstream and template caps does
not contain a specific annex it will be not added to the caps. Previous
behavior was that it was set explictily to false.

This fixes an issue if an encoder (avenc_h263p) is linked late with the
payloader it could end up as not negotiated.

pexip/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good