test: remove message from assert.strictEqual()

Converted the 'message' argument values from the last two free socket
assert.strictEqual() calls to code comments as they fail to provide the
necessary details and values specific to why the test is failing. The
default message returned from the strictEqual() call should provide
sufficient details for debugging errors.

PR-URL: #19525
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-http-agent-error-on-idle.js

@@ -27,8 +27,8 @@ server.listen(0, () => {
    res.on('end', common.mustCall(() => {
      process.nextTick(common.mustCall(() => {
        const freeSockets = agent.freeSockets[socketKey];
        assert.strictEqual(freeSockets.length, 1,
                           `expect a free socket on ${socketKey}`);
        //expect a free socket on socketKey
        assert.strictEqual(freeSockets.length, 1);

        //generate a random error on the free socket
        const freeSocket = freeSockets[0];
@@ -40,8 +40,8 @@ server.listen(0, () => {
  }));

  function done() {
    assert.strictEqual(Object.keys(agent.freeSockets).length, 0,
                       'expect the freeSockets pool to be empty');
    //expect the freeSockets pool to be empty
    assert.strictEqual(Object.keys(agent.freeSockets).length, 0);

    agent.destroy();
    server.close();