Removes unticked unused code from the tree

You can always use git history if you need them for some reason, so there is no point in keeping these in the current tree. All the deleted code was unticked.

### Deleted
1. code/_onclick/oldcode.dm
2. code/game/mecha/equipment/tools/unused_tools.dm
3. all of code/unused
4. most of code/WorkInProgress
    * buildmode.dm and explosion_particles.dm are ticked and thus were moved to proper folders