Rename `core` to `minetest` (#2552)

.luacheckrc

@@ -3,7 +3,7 @@ allow_defined_top = true
 
 read_globals = {
 	"DIR_DELIM",
-	"minetest", "core",
+	"minetest",
 	"dump",
 	"vector",
 	"VoxelManip", "VoxelArea",

mods/game_commands/init.lua

@@ -13,7 +13,7 @@ minetest.register_chatcommand("killme", {
 				player:set_hp(0)
 				return true
 			else
-				for _, callback in pairs(core.registered_on_respawnplayers) do
+				for _, callback in pairs(minetest.registered_on_respawnplayers) do
 					if callback(player) then
 						return true
 					end