Make mesechest more reliable (#35)

The current hack to get on the `on_player_receive_fields` function is quite likely to break with instrumented code.
This also changes the workaround to get custom inventory callbacks by using `minetest.override_item`.

.luacheckrc

@@ -1,22 +1,9 @@
 read_globals = {
 	-- Defined by Minetest
-	"vector", "PseudoRandom", "VoxelArea", "table",
+	"minetest", "vector", "PseudoRandom", "VoxelArea", "table",
 
 	-- Mods
 	"digiline", "default", "creative",
-
-	-- Required for the mesechest registration
-	minetest = {
-		fields = {
-			register_lbm = {read_only = false},
-			register_node = {read_only = false},
-			registered_on_player_receive_fields = {
-				read_only = false,
-				other_fields = true,
-			},
-		},
-		other_fields = true
-	}
 }
 globals = {"moremesecons", "mesecon"}
 ignore = {"212", "631", "422", "432"}