Use new soong support to install privapp xml

This allows better overriding of it in the variants of this apex
that have a different package name.

Bug: 242509786
Test: build google tethering, diff before & after
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:91442c93fb8d7f67bf90faab0552428ff07f0452)
Merged-In: I84c53458686f70408ec759df854f5fcdee9cdaed
Change-Id: I84c53458686f70408ec759df854f5fcdee9cdaed
diff --git a/Tethering/apex/Android.bp b/Tethering/apex/Android.bp
index 4bfd1fb..cf9b359 100644
--- a/Tethering/apex/Android.bp
+++ b/Tethering/apex/Android.bp
@@ -112,10 +112,7 @@
         "ServiceConnectivityResources",
         "HalfSheetUX",
     ],
-    prebuilts: [
-        "current_sdkinfo",
-        "privapp_allowlist_com.android.tethering",
-    ],
+    prebuilts: ["current_sdkinfo"],
     manifest: "manifest.json",
     key: "com.android.tethering.key",
     // Indicates that pre-installed version of this apex can be compressed.