Simplify async streaming solution per PR comment.

Author: michaelsafyan

instrumentation-genai/opentelemetry-instrumentation-google-genai/src/opentelemetry/instrumentation/google_genai/generate_content.py

@@ -668,11 +668,7 @@ async def _response_async_generator_wrapper():
                 finally:
                     helper.finalize_processing()
 
-        class _GeneratorProvider:
-            def __aiter__(self):
-                return _response_async_generator_wrapper()
-
-        return _GeneratorProvider()
+        return _response_async_generator_wrapper()
 
     return instrumented_generate_content_stream