Remove support for EXPERIMENTAL_JAVA_LANGUAGE_LEVEL_9.

Prior to this change, setting that to "false" turned the default Java
language level back to 8. This change removes that option.

Bug: 115604102
Test: m java droid docs tests cts
Change-Id: I97bfd0dc8d941008b4071c6efe1c0c24950c4f1f
diff --git a/java/java.go b/java/java.go
index be48256..71d0098 100644
--- a/java/java.go
+++ b/java/java.go
@@ -884,7 +884,7 @@
 		ret = normalizeJavaVersion(ctx, javaVersion)
 	} else if ctx.Device() && sdk <= 23 {
 		ret = "1.7"
-	} else if ctx.Device() && sdk <= 29 || !ctx.Config().TargetOpenJDK9() {
+	} else if ctx.Device() && sdk <= 29 {
 		ret = "1.8"
 	} else if ctx.Device() &&
 		sdkContext.sdkVersion() != "" &&