Use scopeguard from libbase_headers and delete the copy

A recent change makes libbase_headers available to the tethering apex.

Test: m
Change-Id: Id4f30f48bd65175e17c419230a8e7ebf5339d713
diff --git a/Tethering/Android.bp b/Tethering/Android.bp
index 19bcff9..e84573b 100644
--- a/Tethering/Android.bp
+++ b/Tethering/Android.bp
@@ -126,7 +126,7 @@
 // Due to b/143733063, APK can't access a jni lib that is in APEX (but not in the APK).
 cc_library {
     name: "libcom_android_networkstack_tethering_util_jni",
-    sdk_version: "30",
+    sdk_version: "current",
     apex_available: [
         "com.android.tethering",
     ],