tests(ag-ui): fix duplicate import

Remove duplicate import added by AI refactor of the package name causing
failures when the package is not installed.

Author: stevenh

tests/test_ag_ui.py

@@ -12,7 +12,6 @@
 
 from pydantic_ai import Agent
 from pydantic_ai.models.test import TestModel
-from pydantic_ai_ag_ui.adapter import Adapter
 
 has_required_python: bool = sys.version_info >= (3, 10)
 has_ag_ui: bool = False