TTT: Fix ENT:Disarm() getting called clientside

Fixes when the entity moves further than MAX_MOVE_RANGE it'll try to call the serverside method ENT:Disarm() clientside causing:

[ERROR] gamemodes/terrortown/entities/entities/ttt_c4/shared.lua:308: attempt to call method 'Disarm' (a nil value)
1. unknown - gamemodes/terrortown/entities/entities/ttt_c4/shared.lua:308