lineage: configs: Flatten APEX(s) on official builds

* APEX is useless to average Lineage user, as we aren't
  licensed to ship the GMS APEX's, nor would we want to,
  as we want to keep compatibility with non-GMS use-cases.

* Additionally, APEX's should each be signed with their
  own unique key, and number of them can vary per-device,
  which makes signing them in a standard way on infrastructure
  quite complex.

* Though this flag is default, we need to disable it
  explicitly to make sure any maintainers who set up the
  configurations for APEX images won't change needs of
  infrastructure. This will allow people who want to build
  locally to use full APEX(s).

Change-Id: I7f2eb52593eeca1b3761a7a163ce9079995870c6