iotests: drop compat for old version context manager

Our minimum python is now 3.9, so back compat with prior
python versions is no longer required.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

tests/qemu-iotests/testenv.py

@@ -22,15 +22,12 @@ import tempfile
 from pathlib import Path
 import shutil
 import collections
+import contextlib
 import random
 import subprocess
 import glob
 from typing import List, Dict, Any, Optional
 
-if sys.version_info >= (3, 9):
-    from contextlib import AbstractContextManager as ContextManager
-else:
-    from typing import ContextManager
 
 DEF_GDB_OPTIONS = 'localhost:12345'
 
@@ -58,7 +55,7 @@ def get_default_machine(qemu_prog: str) -> str:
     return default_machine
 
 
-class TestEnv(ContextManager['TestEnv']):
+class TestEnv(contextlib.AbstractContextManager['TestEnv']):
     """
     Manage system environment for running tests
 

tests/qemu-iotests/testrunner.py

@@ -30,11 +30,6 @@ from multiprocessing import Pool
 from typing import List, Optional, Any, Sequence, Dict
 from testenv import TestEnv
 
-if sys.version_info >= (3, 9):
-    from contextlib import AbstractContextManager as ContextManager
-else:
-    from typing import ContextManager
-
 
 def silent_unlink(path: Path) -> None:
     try:
@@ -57,7 +52,7 @@ def file_diff(file1: str, file2: str) -> List[str]:
         return res
 
 
-class LastElapsedTime(ContextManager['LastElapsedTime']):
+class LastElapsedTime(contextlib.AbstractContextManager['LastElapsedTime']):
     """ Cache for elapsed time for tests, to show it during new test run
 
     It is safe to use get() at any time.  To use update(), you must either
@@ -112,7 +107,7 @@ class TestResult:
         self.interrupted = interrupted
 
 
-class TestRunner(ContextManager['TestRunner']):
+class TestRunner(contextlib.AbstractContextManager['TestRunner']):
     shared_self = None
 
     @staticmethod