userland: fix installed-vs-shipped in multilib builds

Be aware that whole userland repo is marked as ancient and deprecated:
raspberrypi/userland@96a7334
and explicitly says:
"If you are using code from here you should rethink your solution."

But even if your build is using vc4graphics in MACHINE_FEATURES
to avoid most of userland, this issue with multilib was preventing
do_install:append to actually remove those libraries provided by
lib32-mesa when building lib32-userland (e.g. to provide
virtual/libomxil or as dependency of raspidmx or runtime dependency
of omxplayer).

Signed-off-by: Martin Jansa <[email protected]>