Returns if the given NPC class name is an enemy.

Returns true if the entity name is one of the following:

• "npc_antlion"
• "npc_antlionguard"
• "npc_antlionguardian"
• "npc_barnacle"
• "npc_breen"
• "npc_clawscanner"
• "npc_combine_s"
• "npc_cscanner"
• "npc_fastzombie"
• "npc_fastzombie_torso"
• "npc_headcrab"
• "npc_headcrab_fast"
• "npc_headcrab_poison"
• "npc_hunter"
• "npc_metropolice"
• "npc_manhack"
• "npc_poisonzombie"
• "npc_strider"
• "npc_stalker"
• "npc_zombie"
• "npc_zombie_torso"
• "npc_zombine"