Fix and enable collateral damage for missing missiles

Fix and enable collateral damage for missing missiles

Collateral damage was disabled, because after msl_hit() reported a
miss, the missile may or may not have reached the target.

Fix by splitting msl_launch() off msl_hit().

Drop the disabled collateral damage code for sector targets, because
sectors can't be missed.  Enable it for ships and land units.

Since msl_launch() returns whether the missile is sub-launched, drop
launch_missile() parameter sublaunch, and simplify its caller.