Simplify IMMS#getEnabledInputMethodSubtypeList() a bit

This is a follow up CL to my previous CL [1], which let query APIs
defined in InputMethodManager support background users.

Basically UserHandle.getCallingUserId() never returns a pseudo user ID
such as UserHandle#USER_CURRENT.  Hence there is no need to use
InputMethodUtils.resolveUserId there.

There should be no developer observable behavior change.

 [1]: I192a0f5a1375170d17a4c08af94f23966dbaea8b
      7f8ee4b9dd

Bug: 122164939
Bug: 234882948
Test: make -j CtsInputMethod1  \
                CtsInputMethod2  \
                CtsInputMethodServiceDeviceTests  \
                CtsInputMethodServiceEventProvider  \
                CtsInputMethodServiceHostTestCases  \
                EditTextApp  &&
        atest CtsInputMethodServiceHostTestCases
Change-Id: I85da7d819b6fba01fce1e5df1347534febf9aa53

services/core/java/com/android/server/inputmethod/InputMethodManagerService.java

@@ -2208,15 +2208,10 @@ public final class InputMethodManagerService extends IInputMethodManager.Stub
             boolean allowsImplicitlySelectedSubtypes) {
         final int callingUserId = UserHandle.getCallingUserId();
         synchronized (ImfLock.class) {
-            final int[] resolvedUserIds = InputMethodUtils.resolveUserId(callingUserId,
-                    mSettings.getCurrentUserId(), null);
-            if (resolvedUserIds.length != 1) {
-                return Collections.emptyList();
-            }
             final long ident = Binder.clearCallingIdentity();
             try {
                 return getEnabledInputMethodSubtypeListLocked(imiId,
-                        allowsImplicitlySelectedSubtypes, resolvedUserIds[0]);
+                        allowsImplicitlySelectedSubtypes, callingUserId);
             } finally {
                 Binder.restoreCallingIdentity(ident);
             }