Enabling "Send collision messages" on a particle system collision module works only for world collisions and not for planar collisions.

Repro steps:
1. Open ShurikenPlaneCollisionTest from attached project
2. Press Play
3. Select the Particle System in the Hierarchy and switch the collision model from plane to world.
4. Observe the word “BAM!” being printed in the console.

Expected outcome: Send collision messages to work in both world and plane collision modes.

Notes:
- not a regression; according to dev it's always been like this. Needs to either be implemented, or the "Send collision messages" checkbox needs to be removed from planar collisions.