Remove FORCE from gpl_source.tgz

Package gpl_source.tgz directly into the dist directory (which is
always removed between build server builds) so that FORCE is not
needed.  This prevents the build system from seeing a dirty rule
at the end of a make checkbuild dist.

Bug: 68062417
Test: m checkbuild dist
Change-Id: I4a9d9deb1611cc9ba266e8c1ac086a7ef48061c4