ci: use separate repo for gc64 packages

It looks like the simplest solution to deliver gc64 tarantool builds
is to have a separate repo for it. So this patch removes old stuff
related to the 'tarantool-gc64' package and adds the new logic to
store gc64 packages in a separate repo.

Closes: tarantool/tarantool-qa#161

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci

Co-authored-by: Yaroslav Lobankov <y.lobankov@tarantool.org>