test: connection leak test test_discovery_http_is_closed is shadowed and syntactically invalid

### **Environment details**

- OS type and version: Linux (gLinux / Debian based)
- Python version: `3.13.12` (also affects all supported Python versions `3.10+`)
- pip version: `26.0.1`
- `google-api-python-client` version: `2.197.0` (at commit `6e471c075039dfef24e28d11658e03d5c949c7c3`)

---

### **Steps to reproduce**

1. Look at `tests/test_discovery.py` on `main`. Note that there are **two separate definitions** for `class Discovery(unittest.TestCase)` (one at line 498 and one at line 1566).
2. In Python, defining a class twice in the same module causes the second definition to silently overwrite the first. This means the first `Discovery` class—which contains the test case **`test_discovery_http_is_closed`**—is completely dead code and is never executed by `pytest`.
3. Attempting to manually extract and execute this test case crashes immediately because `HttpMock.close()` is a regular function, but the test tries to call `assert_called_once()` on it.

---

### **Code example**

The shadowed class in `tests/test_discovery.py` contains this test definition:
```python
class Discovery(unittest.TestCase):
def test_discovery_http_is_closed(self):
http = HttpMock(datafile("malformed.json"), {"status": "200"})
# build() is called without passing the 'http' mock client!
service = build("plus", "v1", credentials=mock.sentinel.credentials)
# Fails: HttpMock.close is a standard method, not a mock object
http.close.assert_called_once()
```

#### **Historical Context**
This bug was introduced in **September 2020** by commit **`98888dadf`** ("fix: add method to close httplib2 connections (#1038)").
That commit added `test_discovery_http_is_closed` by declaring a new `class Discovery(unittest.TestCase)` block near the top of the file, without realizing that a `class Discovery(unittest.TestCase)` block was already defined and active near the bottom of the file (which immediately shadowed the new test).

#### **The Proposed Solution**
1. Delete the duplicate class definition at line 498.
2. Restore `test_discovery_http_is_closed` inside the active `Discovery` class (at line 1566).
3. Correct the test case to use standard `unittest.mock.patch` on `httplib2.Http` to verify that the temporary HTTP client created by `build()` to fetch the discovery document is safely closed after initialization completes, preventing connection/socket leaks.

```python
@mock.patch("httplib2.Http")
def test_discovery_http_is_closed(self, mock_http_class):
mock_http = mock_http_class.return_value
mock_http.request.return_value = (
httplib2.Response({"status": "200"}),
read_datafile("plus.json"),
)
service = build("plus", "v1", static_discovery=False)
mock_http.close.assert_called_once()
```

---

### **Stack trace**

If you isolate the legacy test case and run it, it crashes immediately with an `AttributeError`:

```
AttributeError: 'function' object has no attribute 'assert_called_once'
```