Remove InputMethodManagerDelegate#startInput()

This is a follow up CL to my previous CL [1], which partly reverted
the initial commit of ImeFocusController [2].

With that CL,

  InputMethodManagerDelegate#startInput()

is no longer called.  Thus we no longer need to defined it.

There must be no behavior change.

 [1]: Ie3446e1d0f62c489195e31fc7f073020884d6cae
      ff975479b4f60fe1c599826dd6f42f24a42883f9
 [2]: Ib455704fe1e9d243f93190a84f230210dbceac2a
      970d9d2e0c979cf9a0ff0a79ef49044ed1363d4f

Bug: 234882948
Bug: 244504062
Test: presubmit
Change-Id: I62ae648b75cc33592e4e985b4c975c97ccdd24f8
diff --git a/core/java/android/view/ImeFocusController.java b/core/java/android/view/ImeFocusController.java
index 1afd048..4e162f5 100644
--- a/core/java/android/view/ImeFocusController.java
+++ b/core/java/android/view/ImeFocusController.java
@@ -26,8 +26,6 @@
 import android.view.inputmethod.InputMethodManager;
 
 import com.android.internal.inputmethod.InputMethodDebug;
-import com.android.internal.inputmethod.StartInputFlags;
-import com.android.internal.inputmethod.StartInputReason;
 
 /**
  * Responsible for IME focus handling inside {@link ViewRootImpl}.
@@ -189,13 +187,6 @@
      * @hide
      */
     public interface InputMethodManagerDelegate {
-        /**
-         * Starts the input connection.
-         */
-        boolean startInput(@StartInputReason int startInputReason, View focusedView,
-                @StartInputFlags int startInputFlags,
-                @WindowManager.LayoutParams.SoftInputModeFlags int softInputMode, int windowFlags);
-
         void onPostWindowFocus(View viewForWindowFocus,
                 @NonNull WindowManager.LayoutParams windowAttribute);
         void onViewFocusChanged(@NonNull View view, boolean hasFocus);
diff --git a/core/java/android/view/inputmethod/InputMethodManager.java b/core/java/android/view/inputmethod/InputMethodManager.java
index 08a7583..2e8ee77 100644
--- a/core/java/android/view/inputmethod/InputMethodManager.java
+++ b/core/java/android/view/inputmethod/InputMethodManager.java
@@ -737,11 +737,8 @@
 
     private final class DelegateImpl implements
             ImeFocusController.InputMethodManagerDelegate {
-        /**
-         * Used by {@link ImeFocusController} to start input connection.
-         */
-        @Override
-        public boolean startInput(@StartInputReason int startInputReason, View focusedView,
+
+        private boolean startInput(@StartInputReason int startInputReason, View focusedView,
                 @StartInputFlags int startInputFlags, @SoftInputModeFlags int softInputMode,
                 int windowFlags) {
             ImeTracing.getInstance().triggerClientDump(