Revert: Rework unit loading to take into account all aliases

Revert: Rework unit loading to take into account all aliases

Revert below patches due to increasing unit loading time (UnitsLoadFinishTimestamp - UnitsLoadStartTimestamp)

Refer: https://github.com/systemd/systemd/pull/13119/commits
 - test-unit-file: allow printing of information about specific units
 - pid1: drop unit caches only based on mtime
 - analyze: add "unit-files" to dump the unit fragment map
 - core: restore initialization of u->source_mtime
 - pid1: use a cache for all unit aliases
 - shared/unit-file: add a function to validate unit alias symlinks
 - TEST-15-DROPIN: add test for details of unit aliasing

Change-Id: I1bff89f5851544cda7522bd3ceb398499dac57d4