Remove @UnsupportedAppUsage from InputMethodManager#getClient()

We are mostly confident that this @UnsupportedAppUsage was a false
positive.

Bug: 78484047
Fix: 194333155
Test: presubmit
Change-Id: I47f3a5438bad6c8fa386b68ae7ac918a5c3e5d71

core/java/android/view/inputmethod/InputMethodManager.java

@@ -1202,8 +1202,14 @@ public final class InputMethodManager {
         }
     }
 
-    /** @hide */
-    @UnsupportedAppUsage
+    /**
+     * No longer used.  Do not use.
+     *
+     * TODO(b/192412909) Remove this method.
+     *
+     * @deprecated Was kept due to {@link UnsupportedAppUsage}.  Will be removed soon.
+     * @hide
+     */
     public IInputMethodClient getClient() {
         return mClient;
     }