UT: Remove patch_get_agent_id()

1. This fixture was never actually executing
2. get_agent_id() always returns the same value (per process). This
   means that _get_ping_scan_event() and the ping scanner will receive
   the same value for any given test. In other words, mocking it is
   unnecessary.

monkey/tests/unit_tests/infection_monkey/network_scanning/test_ping_scanner.py

@@ -1,7 +1,6 @@
 import math
 import subprocess
 from unittest.mock import MagicMock
-from uuid import UUID
 
 import pytest
 
@@ -56,11 +55,6 @@ ttl=2d2!
 """
 
 
-@pytest.fixture(scope="module")
-def patch_get_agent_id(monkeypatch):
-    monkeypatch.setattr("get_agent_id", lambda: UUID("9919520c-8650-4a39-aa1e-b2f4d1445159"))
-
-
 TIMESTAMP = 123.321