chore(llmobs): revert "feat(llmobs): openai agents sdk integration" (#13080)

Revert #12846 if i dont find a fix soon for OOM ci
failures for `llmobs::openai_agents 4/4`. Currently trying
#13079


https://gitlab.ddbuild.io/DataDog/apm-reliability/dd-trace-py/-/jobs/882041531

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Author: lievan

.riot/requirements/14e7a10.txt

@@ -109,7 +109,6 @@
     "coverage": False,
     "selenium": True,
     "valkey": True,
-    "openai_agents": True,
 }
 
 
@@ -159,7 +158,6 @@
         "langgraph",
         "langgraph.graph",
     ),
-    "openai_agents": ("agents",),
 }
 
 _NOT_PATCHABLE_VIA_ENVVAR = {"ddtrace_api"}