refactor(pyoaev): deleting unused retro-compatibility (#217)

Dependency was a transitive one + pyproject points out 3.11 as min
version

Author: guzmud

pyoaev/backends/protocol.py

@@ -1,15 +1,9 @@
 import abc
-import sys
-from typing import Any, Dict, Optional, Union
+from typing import Any, Dict, Optional, Protocol, Union
 
 import requests
 from requests_toolbelt.multipart.encoder import MultipartEncoder  # type: ignore
 
-if sys.version_info >= (3, 8):
-    from typing import Protocol
-else:
-    from typing_extensions import Protocol
-
 
 class BackendResponse(Protocol):
     @abc.abstractmethod