FS-8867: build using in tree libvpx, vpx no longer optional and does not use system...

FS-8867: build using in tree libvpx, vpx no longer optional and does not use system libvpx due to issues with having to update it frequently conflicting with system libraries, now we link to the static in tree version instead.  Also, mod_vpx is now a core module instead of a loadable module, so mod_vpx.so will no longer be built