Refactor request teardown to avoid duplicate cleanup

Remove redundant environment variable cleanup in finally block.

Author: 123liuziming

instrumentation/opentelemetry-instrumentation-flask/src/opentelemetry/instrumentation/flask/__init__.py

@@ -643,6 +643,8 @@ def _teardown_request(exc):
 
             if token:
                 context.detach(token)
+                flask.request.environ.pop(_ENVIRON_ACTIVATION_KEY, None)
+                flask.request.environ.pop(_ENVIRON_TOKEN, None)
 
         except (RuntimeError, AttributeError, ValueError) as teardown_exc:
             # Log the error but don't raise it to avoid breaking the request handling
@@ -651,9 +653,6 @@ def _teardown_request(exc):
                 teardown_exc,
                 exc_info=True,
             )
-        finally:
-            flask.request.environ.pop(_ENVIRON_ACTIVATION_KEY, None)
-            flask.request.environ.pop(_ENVIRON_TOKEN, None)
 
     return _teardown_request