Split "Paradrop Unit"
Targets 3.1 because Unit:perform_action(find.action("Paradrop Unit"), target_tile) - new in 3.1 - will expect certain side effects if they are there in 3.1.
Allows more fine grained control over Paradrop side effects. Enables simplifications and clean ups already half way done 3.1. Avoids backwards compatibility problems from Unit:perform_action() starting to depend on side effects.
Allows removing its hard coded side effect rules.