Don't build android.test.mock.stubs for unbundled builds

Unbundled builds use the prebuilt libs in /prebuilts/sdk/current and
system_current.

Bug: 73829976
Test: m -j ANDROID_BUILDSPEC=vendor/google/build/app_build_spec.mk

Change-Id: I61fe0d671778595f49be82d7c11caffc411f58a3

test-mock/Android.bp

@@ -84,10 +84,24 @@ java_library_static {
     name: "android.test.mock.stubs",
     srcs: [":android.test.mock.docs"],
     sdk_version: "current",
+    product_variables: {
+        unbundled_build: {
+            // Unbundled apps will use the prebuilt one
+            // prebuilts/sdk/current
+            enabled: false,
+        },
+    },
 }
 
 java_library_static {
     name: "android.test.mock.stubs-system",
     srcs: [":android.test.mock.docs-system"],
     sdk_version: "system_current",
+    product_variables: {
+        unbundled_build: {
+            // Unbundled apps will use the prebuilt one
+            // prebuilts/sdk/system_current
+            enabled: false,
+        },
+    },
 }