Use the RELEASE_TARGET_JAVA_21 flag for makefiles

Bug: 342332820
Test: m
Change-Id: Icefae0658b40b9f50726e497c4518717ddfdbb1a
diff --git a/core/java_common.mk b/core/java_common.mk
index a21f062..f574b76 100644
--- a/core/java_common.mk
+++ b/core/java_common.mk
@@ -32,7 +32,7 @@
     else ifneq (,$(LOCAL_SDK_VERSION)$(TARGET_BUILD_USE_PREBUILT_SDKS))
       # TODO(ccross): allow 1.9 for current and unbundled once we have SDK system modules
       LOCAL_JAVA_LANGUAGE_VERSION := 1.8
-    else ifeq ($(EXPERIMENTAL_TARGET_JAVA_VERSION_21),true)
+    else ifeq ($(RELEASE_TARGET_JAVA_21),true)
       LOCAL_JAVA_LANGUAGE_VERSION := 21
     else
       LOCAL_JAVA_LANGUAGE_VERSION := 17