Fix starting abilities duplicating onto remaining molehills

[JeodC]

Enabling a starting ability erased its molehill from abilityCheckPool but left the matching ability in abilityItemPool, so the two pools desynced. The already-owned ability stayed eligible and could win the roll for one of the remaining molehills, pushing an ability that was actually needed out of the seed. Starting with everything except Talon Trot could leave Talon Trot unplaced entirely, making a glitchless seed unbeatable.

reachableChecks[].isShuffled was also marked before the loadout erase and never cleared, so an erased molehill was still a valid placement target for GetRandomCheckIndexS. An ability placed there was silently dropped when GeneratePools rebuilt the pools from abilityCheckPool.

Erase the matching item alongside the molehill, clear isShuffled on the erased check, and reset isShuffled with the rest of reachableChecks so the flag no longer leaks across generations within a session.