Make desugar tests assume android-24.

Previously, they assumed android-25 but Bazel CI does not have android-25
installed. In practice, these tests do not care which version is used so we
should use //tools/android:defaults_jar which selects the jar based on the
configuration. However, that target does not produce the jar as a runfile, it
is only useful currently for neverlink compilation.

RELNOTES: None
PiperOrigin-RevId: 169104539

src/test/java/com/google/devtools/build/android/desugar/BUILD

@@ -20,7 +20,7 @@ filegroup(
     name = "android_jar_for_testing",
     srcs = select({
         # TODO(ajmichael): Use //tools/defaults:android_jar here once it supplies runfiles.
-        "//external:has_androidsdk": ["@androidsdk//:platforms/android-25/android.jar"],
+        "//external:has_androidsdk": ["@androidsdk//:platforms/android-24/android.jar"],
         "//conditions:default": ["@bazel_tools//tools/android:error_message.jar"],
     }),
 )