openai-v2: try dropping datalib optional dependencies from requirements

Since they slow down tests.

Author: xrmx

instrumentation-genai/opentelemetry-instrumentation-openai-v2/tests/requirements.oldest.txt

@@ -15,7 +15,7 @@
 # This variant of the requirements aims to test the system using
 # the oldest supported version of external dependencies.
 
-openai[datalib]==1.26.0
+openai==1.26.0
 pydantic==2.8.2
 httpx==0.27.2
 Deprecated==1.2.14