Delete old TEXT_SELECTION_MENU_ITEM_ASSIST logs.

This field is now being used for new smart selection logging.
See: Icc9d5b542140bdb01b2ad4211048bd83eae2ce83

Bug: 64914512
Test: bit FrameworksCoreTests:android.widget.TextViewActivityTest
Test: bit CtsWidgetTestCases:android.widget.cts.TextViewTest
Test: bit CtsAccessibilityServiceTestCases:android.accessibilityservice.cts.AccessibilityTextTraversalTest
Change-Id: If1ce8ca038b089500cd7adb9a146330abe909407