Revert "Enable prebuilt SDK."

This reverts commit fd89f5ab.

Bug: 192588050
Change-Id: I1704e4f1384ef1f6f2606a07bfe5c8a2faa1e7c5

current/Android.bp

@@ -24,7 +24,7 @@ prebuilt_bootclasspath_fragment {
 
 prebuilt_bootclasspath_fragment {
     name: "com.android.sdkext-bootclasspath-fragment",
-    prefer: true,
+    prefer: false,
     visibility: ["//packages/modules/SdkExtensions:__subpackages__"],
     apex_available: ["com.android.sdkext"],
     licenses: ["sdkextensions-sdk_Android-Apache-2.0"],
@@ -73,7 +73,7 @@ java_sdk_library_import {
 
 java_sdk_library_import {
     name: "framework-sdkextensions",
-    prefer: true,
+    prefer: false,
     visibility: ["//visibility:public"],
     apex_available: [
         "com.android.sdkext",