Changes the Medtech kit's bonesaw's force from 20 > 15 (#4058)

## About The Pull Request

Title explains it. Goes from 6.7 hits/crit to 9
## Why It's Good For The Game
A circular saw having the damage of more dedicated melee weapons (on par
with the bowie knife/cap's sabre minus the block and AP) whilst also
being pocket sized - AND being included in a medkit just don't make
sense. A little less damage than a regular circular saw is reasonable
given it's more compact. In its current state it does more damage than
the upgraded medical tools. There is very little reason for this to do
as much damage as it does.
## Proof Of Testing
<details>
<summary>Screenshots/Videos</summary>

</details>

## Changelog
🆑
balance: Moved the Bone Saw's force from 20 > 15
/🆑

modular_skyrat/modules/exp_corps/code/gear.dm

@@ -19,7 +19,7 @@
 /obj/item/circular_saw/field_medic
 	name = "bone saw"
 	desc = "Did that sting? SAW-ry!"
-	force = 20
+	force = 15
 	icon_state = "bonesaw"
 	icon = 'modular_skyrat/modules/exp_corps/icons/bonesaw.dmi'
 	lefthand_file = 'modular_skyrat/modules/exp_corps/icons/bonesaw_l.dmi'