fix(vertex): remove anthropic_version deletion for token counting

src/anthropic/lib/vertex/_client.py

@@ -447,9 +447,6 @@ def _prepare_options(input_options: FinalRequestOptions, *, project_id: str | No
                 "No project_id was given and it could not be resolved from credentials. The client should be instantiated with the `project_id` argument or the `ANTHROPIC_VERTEX_PROJECT_ID` environment variable should be set."
             )
 
-        if is_dict(options.json_data):
-            options.json_data.pop("anthropic_version", None)
-
         options.url = f"/projects/{project_id}/locations/{region}/publishers/anthropic/models/count-tokens:rawPredict"
 
     if options.url.startswith('/v1/messages/batches'):