SQLite followup: Remove target tags from stored XML, saving 100kB from .xpi

This changes several things:
 - Fixes `view source XML', which my sqlite branch broke.
 - Removes target tags from XML in DB to save space.
 - Changes targets map in HTTPSRules to contain lists of ruleset ids from DB.
 - Deleted code for reading a full directory of rules, which is no longer called anywhere.