Mining tweaks (#18686)

So we have pickaxe, drill, crusher, and PKA (projectiles).
The tier list in terms of mining speed should go:
- PKA
- Crusher
- Pickaxe
- Drill

As a result:
- Nerfed PKA firerate to 0.5 and bumped damage (slight DPS nerf due to meta).
- Crusher bumped to 1 hit per second as PKA is still more common and also to make it better at mining.
- Pickaxe is 1 hit per second and also gets structural (fireaxe should still beat it by a little bit) so it's better to break stuff than crusher but worse in combat.
- Drill is 1.5 hits per second but otherwise weak.

Content.Shared/Gatherable/GatherableDoAfterEvent.cs

@@ -1,9 +0,0 @@
-using Content.Shared.DoAfter;
-using Robust.Shared.Serialization;
-
-namespace Content.Shared.Gatherable;
-
-[Serializable, NetSerializable]
-public sealed class GatherableDoAfterEvent : SimpleDoAfterEvent
-{
-}