Fix flakiness of test_metric_collection

[bayandin]

Problem

Test test_metric_collection become flaky (an example):

AssertionError: assert not ['2023-05-25T14:03:41.644042Z ERROR metrics_collection: failed to send metrics: reqwest::Error { kind: Request, url: Url { scheme: "http", cannot_be_a_base: false, username: "", password: None, host: Some(Domain("localhost")), port: Some(18022), path: "/billing/api/v1/usage_events", query: None, fragment: None }, source: hyper::Error(Connect, ConnectError("tcp connect error", Os { code: 99, kind: AddrNotAvailable, message: "Cannot assign requested address" })) }',
                            ...]

I suspect it is caused by having 2 places when we define httpserver_listen_address fixture (which is internally used by pytest-httpserver plugin)

@pytest.fixture(scope="session")
def httpserver_listen_address(port_distributor: PortDistributor):
    port = port_distributor.get_port()
    return ("localhost", port)

Summary of changes

• Remove definition of httpserver_listen_address from test_runner/regress/test_ddl_forwarding.py and keep one in test_runner/fixtures/neon_fixtures.py
• Also remote unused httpserver_listen_address parameter from test_proxy_metric_collection

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

1004 tests run: 964 passed, 0 failed, 40 skipped (full report)

---

Flaky tests (3)

Postgres 15

• test_remote_storage_upload_queue_retries[local_fs]: ✅ debug
• test_remote_timeline_client_calls_started_metric[local_fs]: ✅ release
• test_get_tenant_size_with_multiple_branches: ✅ release

_{The comment gets automatically updated with the latest test results
6af13ba at 2023-05-25T19:16:57.851Z :recycle:}

[save-buffer]

Thanks for fixing this! I guess I didn't realize we had a port distributor in neon_fixtures