Previous to dfda2f68 (submodule: remove the per-repo cache,
2015-04-27), we tried to cache our submodules per repository to avoid
having to reload it too frequently. As it created some headaches with
regards to multithreading, we removed that cache.

Previous to that removal, we had to compute what submodule status to
refresh. The mask computation was not removed, though, resulting in
confusing and actually dead code. While it seems like the mask is
currently in use in a conditional, it is not, as we unconditionally
assign to the mask previous to that condition.

Remove all mask computations to clean up stale code.