Remove architecture independent paths from protocols pkgconfig file

libweston-X-protocols.pc is installed to XDG_DATA_DIRS but contains
architecture dependent paths. Use the newly introduced dataonly feature
in meson to remove architecture paths in the pkgconfig file.

Fixes: #269

Signed-off-by: Rohan Garg <rohan.garg@collabora.com>
5 jobs for meson_feature_dataonly in 5 minutes and 32 seconds (queued for 2 seconds)
latest
Status Name Job ID Coverage
  Container Prep
passed container_prep #9811323

00:02:19

 
  Build
passed build-docs #9811325
kvm

00:01:04

passed build-full #9811324
kvm

00:02:46

passed build-no-gl #9811326
kvm

00:01:19

 
  Pages
passed docs-and-coverage #9811327

00:00:27