Revert "fix(xai): accept max_completion_tokens as a supported param"

This reverts commit 4ff251e6b1.

tests/test_litellm/llms/xai/test_xai_chat_transformation.py

@@ -13,7 +13,6 @@ from litellm.types.utils import (
     ModelResponse,
     Usage,
 )
-from litellm.utils import get_optional_params
 
 
 class TestXAIReasoningTokenFolding:
@@ -310,15 +309,3 @@ class TestXAIReportedCost:
             0.0,
             0.0037756,
         )
-
-
-class TestXAIMaxCompletionTokens:
-    def test_max_completion_tokens_is_accepted_and_mapped_to_max_tokens(self):
-        result = get_optional_params(
-            model="grok-4.20-beta",
-            custom_llm_provider="xai",
-            max_completion_tokens=64,
-        )
-
-        assert result["max_tokens"] == 64
-        assert "max_completion_tokens" not in result