Remove obsolete rock override

[kevingranade]

Summary

SUMMARY: None

Purpose of change

As pointed out here: https://www.reddit.com/r/cataclysmdda/comments/eiuyx5/psa_staff_slings_are_more_powerful_if_you_use/ the rock override in blazemod has drifted away from the definition in mainline, and upon examination no longer accomplishes its original goal of turning the rock into an ammunition type as the base type is now an ammunition as well.

Describe the solution

Remove the rock override, which causes the item to revert to default damage and dispersion, and restores the correct effects list.
See

Cataclysm-DDA/data/json/items/ammo.json

Lines 262 to 281 in ace7e39

	"type": "AMMO",
	"id": "rock",
	"symbol": "*",
	"color": "light_gray",
	"name": "rock",
	"description": "A rock the size of a baseball. Makes a decent melee weapon, and is also good for throwing at enemies.",
	"category": "spare_parts",
	"material": "stone",
	"ammo_type": "rock",
	"flags": "TRADER_AVOID",
	"weight": "657 g",
	"volume": "250 ml",
	"bashing": 7,
	"damage": 7,
	"range": 10,
	"dispersion": 14,
	"loudness": 0,
	"to_hit": -2,
	"effects": [ "NEVER_MISFIRES", "NON-FOULING", "RECOVER_80" ],
	"qualities": [ [ "HAMMER", 1 ] ]

for comparison.

Additional context

The count field is also erroneous, as it is specifying the default value.