Mob attackedby / check_block refactor, plus some minor cleanup of attack_x procs (#79563)

## About The Pull Request

- Deletes `spec_attacked_by`
- Elements simple/basic mob attack threshold
- There was a skeleton mob that "mimics armor" but didn't use the actual
mimicing armor thing we have, so I changed that.
- Moves `check_shields` down to the living level, renames it to
`check_block`
 - Martial art blocking is now signalized (only CQC uses it anyways) 
- Cleaned up a bit of `attack_x` procs, but not a lot. Should have an
entire PR dedicated to this .... mess.
 - Deprecates `/obj/item/melee`

## Why It's Good For The Game

Second verse, same as the first. 

- Less bad species related procs. 
- Largely brings a lot of code in line, making combat more consistent
across types.
- Makes it a lot easier to add new code relating to blocking or taking
damage.

## Changelog

🆑 Melbert
refactor: Refactored another large chuck of attack code, primarily
involving melee item attacks and non-human mob attacks. Report if you
see anything weird
fix: Pacifists clicking on simple robots or silicons no longer causes
sparks
fix: Blocked thrown batons are now properly... blocked
/🆑

code/modules/mob/living/basic/basic.dm

@@ -43,8 +43,6 @@
 
 	/// 1 for full damage, 0 for none, -1 for 1:1 heal from that source.
 	var/list/damage_coeff = list(BRUTE = 1, BURN = 1, TOX = 1, CLONE = 1, STAMINA = 0, OXY = 1)
-	///Minimum force required to deal any damage.
-	var/force_threshold = 0
 
 	///Verbs used for speaking e.g. "Says" or "Chitters". This can be elementized
 	var/list/speak_emote = list()