Remove unused supportsSwitchingToShortcutIme attribute

java/res/values/attrs.xml

java/src/com/android/inputmethod/keyboard/KeyboardId.java

...c/com/android/inputmethod/keyboard/KeyboardLayoutSet.java

...rc/com/android/inputmethod/keyboard/KeyboardSwitcher.java

...android/inputmethod/keyboard/emoji/EmojiPalettesView.java

...ndroid/inputmethod/keyboard/internal/KeyboardBuilder.java

java/src/com/android/inputmethod/latin/InputAttributes.java

java/src/com/android/inputmethod/latin/LatinIME.java

...om/android/inputmethod/latin/settings/SettingsValues.java

...roid/inputmethod/keyboard/KeyboardLayoutSetTestsBase.java

...id/inputmethod/keyboard/layout/tests/LayoutTestsBase.java