gitlab-ci: Remove cmake cache before building in csbuild

This avoids csbuild failures due to new source files added. Previously
in some runs, csbuild would try to reuse the existing cmake cache file
which could contain added dependencies to new source files, leading to
failure in the run.

Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>