Fix delete item action in tests

Tests are using clickToolbarItem on action_menu_delete, which now moves to the overflow menu when the Documents trash feature flag is enabled. The logic has been moved to a single place, clickDelete(), to handle these cases.

Flag: com.android.documentsui.flags.enable_trash_flow_ro
Bug: 441158597
Bug: 441142646
Bug: 441154875
Bug: 441119354
Bug: 441118284
Bug: 441118268
Test: atest DocumentsUIGoogleTests
Change-Id: Ie0fb57ebac148d8e0ad566d9ab8addd7edf4c189