Remove inventoryImports plugin

Remove defunct and coding horror inventoryImports.  The functionality
provided in it should be added as an optional extra to subspace_storage.

test/lib/object_ops.js

@@ -1,22 +0,0 @@
-"use strict";
-var assert = require("assert");
-var libObjectOps = require("@clusterio/lib/object_ops");
-
-describe("lib/object_ops", function(){
-	describe("deepclone()", function(){
-		it("deep clones javascript objects", function(){
-			var obj1 = { hello: "world", cat: { legs: 4, name: "Kitty", colors: ["brown", "yellow", "purple"] }};
-			var obj2 = {};
-			obj2 = libObjectOps.deepclone(obj1);
-
-			obj1.cat.colors = "black";
-			assert.equal(obj1.cat.colors, "black");
-			assert.equal(obj2.cat.colors[1], "yellow");
-		});
-		it("throws on non JSON parameters", function(){
-			assert.throws(function(){
-				let y = libObjectOps.deepclone(libObjectOps.deepclone);
-			});
-		});
-	});
-});