Remove InputMethodManager.ImeThreadFactory, which is unused

InputMethodManager.ImeThreadFactory was originally introduced to fix
Bug 147331480 but all its usages were already removed by a subsequent
CL [2], which somehow forgot to remove this class.

Anyways, this class is definitely unused right now hence it should be
safe for us to remove it.

 [1]: I10391b834c33458c3e0ac846ab738e805d235c26
      ba400449e1
 [2]: Id73f0d5efb68bb4c5c8ef3dfb974c7a4f9457581
      08e9134546

Bug: 171827834
Test: presubmit
Change-Id: I4d1a24be1272670b89b1435f6fd6ff196a22385f

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

@@ -115,7 +115,6 @@ import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 import java.util.concurrent.CountDownLatch;
-import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 
 /**
@@ -1083,19 +1082,6 @@ public final class InputMethodManager {
         }
     }
 
-    private static class ImeThreadFactory implements ThreadFactory {
-        private final String mThreadName;
-
-        ImeThreadFactory(String name) {
-            mThreadName = name;
-        }
-
-        @Override
-        public Thread newThread(Runnable r) {
-            return new Thread(r, mThreadName);
-        }
-    }
-
     final IInputMethodClient.Stub mClient = new IInputMethodClient.Stub() {
         @Override
         protected void dump(FileDescriptor fd, PrintWriter fout, String[] args) {