Conditionally include VCN in Tethering module

When the build system flag RELEASE_MOVE_VCN_TO_MAINLINE is true,
VCN framework lib will be included in the tethering boot classpath
fragment and the VCN service lib will be included in the
service-connectivity.jar

Bug: 375213246
Test: flag enabled: VCN libs are in the tethering module
      flag disabled: VCN libs are in the platform
Flag: RELEASE_MOVE_VCN_TO_MAINLINE
Change-Id: If0239eb1684b861b63794762915dab0d62379885
diff --git a/framework/Android.bp b/framework/Android.bp
index a93a532..7261178 100644
--- a/framework/Android.bp
+++ b/framework/Android.bp
@@ -143,6 +143,7 @@
 java_library {
     name: "framework-connectivity-pre-jarjar",
     defaults: ["framework-module-defaults"],
+    installable: false,
     min_sdk_version: "30",
     static_libs: [
         "framework-connectivity-pre-jarjar-without-cronet",