Target Java 21 by default

Bug: 342332820
Test: TH
Change-Id: I3d440c79231cc470013610c8b3ec95a0b4a0cb6a
diff --git a/android/config.go b/android/config.go
index 16d77db..2a0d810 100644
--- a/android/config.go
+++ b/android/config.go
@@ -867,7 +867,7 @@
 }
 
 func (c *config) TargetsJava21() bool {
-	return c.IsEnvTrue("EXPERIMENTAL_TARGET_JAVA_VERSION_21")
+	return c.productVariables.GetBuildFlagBool("RELEASE_TARGET_JAVA_21")
 }
 
 // EnvDeps returns the environment variables this build depends on. The first