test: remove gemini_cli references in 6 + delete test_ai_client_list_models.py

Drop stale gemini_cli expectations: PROVIDERS expectations in
test_providers_source_of_truth + test_provider_curation, the
test_list_models_gemini_cli function (deleted the whole file since it
was the only test), the test_discussion_compression_gemini_cli function,
the test_gcli_path_updates_adapter function (its setter was removed),
the ui_gemini_cli_path references in test_mma_tier_usage_reset_fix and
test_rag_integration. These are the t1.9 minor edits.

tests/test_process_pending_gui_tasks.py

@@ -36,16 +36,6 @@ def test_redundant_calls_in_process_pending_gui_tasks(app_instance: App) -> None
   assert mock_set_provider.call_count == 1
   assert mock_reset_session.call_count == 1
 
-def test_gcli_path_updates_adapter(app_instance: App) -> None:
- app_instance.controller.current_provider = 'gemini_cli'
- app_instance.controller._pending_gui_tasks = [
-  {'action': 'set_value', 'item': 'gcli_path', 'value': '/new/path/to/gemini'}
- ]
- # Initialize adapter if it doesn't exist (it shouldn't in mock env)
- ai_client._gemini_cli_adapter = None
- app_instance.controller._process_pending_gui_tasks()
- assert ai_client._gemini_cli_adapter is not None
- assert ai_client._gemini_cli_adapter.binary_path == '/new/path/to/gemini'
 
 def test_process_pending_gui_tasks_drag(app_instance: App) -> None:
  """Test that the drag action is correctly processed and dispatches to the registered callback."""