AML: Make UserHandle.myUserId() available

Since the method UserHandle.myUserId() is a @SystemApi, build error
happens when building the mainline module.

This CL makes it available by building the APK with the system SDK.

Bug: 119749861
Test: mmm . (under frameworks/av/packages/MediaComponents)
Change-Id: Iedecf1a7c7de1279161601c1e88f959e89af73ac
diff --git a/packages/MediaComponents/apex/Android.bp b/packages/MediaComponents/apex/Android.bp
index 363a416..e797e14 100644
--- a/packages/MediaComponents/apex/Android.bp
+++ b/packages/MediaComponents/apex/Android.bp
@@ -20,7 +20,7 @@
 java_library {
     name: "media",
     installable: true,
-    sdk_version: "current",
+    sdk_version: "system_current",
     srcs: [
         "java/android/media/**/*.java",
         "java/android/service/**/*.java",