libpacman: Rework a little falgorithm and drop f_ptrlist_clear.
libpacman: Drop FVisitor.
libpacman: Move flib::remove* to FList::remove.

* Returning number of remove is only possible in class, since removing from range require turning the new first element of the range.
* Converting pmhandle_t::dbs_sync to FList<Database *> since now we provide a simplier remove interface.
libpacman: Remove now unused f_ptrlist_add_sorted _pacman_list_remove.
libpacman: Add f_streq.
libpacman: Add F(String)List::contains and find element access members.
libpacman: Use FStringList::contains where possible.