Remove onToggleSoftInput

As CL[1] removed InputMethodService#onToggleSoftInput since framework
side changed internal protocal to simplify the toggle logic without
this method callback.

Also remove ClientCallbackImpl#onToggleSoftInput for
MultiClientInputMethod sample app part to sync this change.

[1]: I390dc029e7bcc30c200926a9bfbbbd0268a1f714

Bug: 182071625
Test: build MultiClientInputMethod
Change-Id: I25568d9d0a963562fdc1d4a021f7016689b9ca54

samples/MultiClientInputMethod/src/com/example/android/multiclientinputmethod/ClientCallbackImpl.java

@@ -197,13 +197,6 @@ final class ClientCallbackImpl implements MultiClientInputMethodServiceDelegate.
         mInputMethod.mDisplayToLastClientId.put(mSelfReportedDisplayId, mClientId);
     }
 
-    @Override
-    public void onToggleSoftInput(int showFlags, int hideFlags) {
-        // TODO: Implement
-        Log.w(TAG, "onToggleSoftInput is not yet implemented. clientId=" + mClientId
-                + " showFlags=" + showFlags + " hideFlags=" + hideFlags);
-    }
-
     @Override
     public void onUpdateCursorAnchorInfo(CursorAnchorInfo info) {
     }