reorg: move js runtime tests to cli/js/tests/ (#4250)

All Deno runtime test files were moved to cli/js/tests/ directory.

It makes a clear distinction that cli/js/tests/ contains code
that is run under Deno runtime as opposed to code in cli/js/ which
is used to create bundle and snapshot with "deno_typescript".

cli/js/internals_test.ts

@@ -1,10 +0,0 @@
-// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
-import { unitTest, assert } from "./test_util.ts";
-
-unitTest(function internalsExists(): void {
-  const {
-    stringifyArgs
-    // @ts-ignore TypeScript (as of 3.7) does not support indexing namespaces by symbol
-  } = Deno[Deno.symbols.internal];
-  assert(!!stringifyArgs);
-});