lib: add sync--filter

[AladW]

With Repo.pm and Depends.pm available, sync could directly access and modify the dependency logic from aur-depends.

Currently the aur-depends --table is modified, which leads to various issues (#1140, #1136).

Only access to AUR::Depends::prune() is needed, which can be done in a helper aur-sync--filter.

[AladW]

#1147