Fix invulnerable sub-carried units

[aeoncleanse]

• Load unit into Stinger
• Load Stinger into any Naval Aircraft Carrier (Czar doesn't work)
• When Carrier dies, we get invulnerable, invisible units capable of attacking

This was caused by the engine Kill() command calling SetDead() before the detach/kill code was called, so the if not self.Dead safety check backfired and prevented the proper handling.

This PR refactors some duplicated loop code, moves it into BaseTransport for inheritance, and adds a Kill() override to AircraftCarrier, fixing the bug.

Please test as many combinations of units inside units inside units as you can think of. Of concern I don't have time to check right now:

• Fatboy
• Air Staging

[PhilipJFryFAF]

tested:

• loading an aurora into a stinger
• loading the stinger with the aurora into an atlantis or czar
• destroying the atlantis/czar via self destruct or instant self destruct

when killing the carrier via instant self destruct we still have the invisible/invincible aurora being left behind

when killing a transport with units loaded via self destruct then the loaded units will not die anymore

will need someone to fix both issues since a) the PR doesn't fix what it says it does and b) introduce a new bug

[shalkya]

i cannot replicate the bug in normal faf.
1- load T2 tank into stinger
2- load stinger into atlantis or aircraft carrier
3- ctrl k aircraft carrier/atlantis (also during the unloading)
4- all units are dead