Grenade GC improvement

[GDNgit]

What Does This PR Do

Improves the GCing on grenades

Why It's Good For The Game

They use walk(), walk is not reset, ref is kept, the grenades will always fail to GC due to this. GCing is good.
This needs to be done for a boatload of other items as well

Testing

compiled, grenades GCed properly.

Changelog

NPFC

[farie82]

Can you show that this actually fixes a GC issue? I'm thinking that walk(src, null, null) works the same as walk(src, 0) due to null and 0 being both falsey

[GDNgit]

Can you show that this actually fixes a GC issue? I'm thinking that walk(src, null, null) works the same as walk(src, 0) due to null and 0 being both falsey

Mirroring from discord:
Grenades use walk_away in a few instances, but most notably in clusterbombs. As those clusterbombs use walk away they will fail to GC, and so will the grenades spawned from the clusterbomb segments.

[farie82]

LGTM besides the small styling thing