node tests: Split up tutorial into smaller examples.

I didn't bother to keep the very last test from
tutorial, which has some complications related
to clearing stream_list data and was kind of
overkill.

frontend_tests/zjsunit/namespace.js

@@ -93,25 +93,6 @@ exports.mock_esm = (request, obj = {}) => {
     return exports.mock_cjs(request, {...obj, __esModule: true});
 };
 
-exports.unmock_module = (request) => {
-    const filename = Module._resolveFilename(
-        request,
-        require.cache[callsites()[1].getFileName()],
-        false,
-    );
-
-    if (!module_mocks.has(filename)) {
-        throw new Error(`Cannot unmock ${filename}, which was not mocked`);
-    }
-
-    if (!used_module_mocks.has(filename)) {
-        throw new Error(`You asked to mock ${filename} but we never saw it during compilation.`);
-    }
-
-    module_mocks.delete(filename);
-    used_module_mocks.delete(filename);
-};
-
 exports.set_global = function (name, val) {
     if (val === null) {
         throw new Error(`