Always use OpenJDK9 for building

Remove support for compiling with javac from OpenJDK8.
We still target 1.8 by default, and OpenJDK8 prebuilts are still
required for the bootclasspath and running robolectric.

Bug: 38418220
Test: m java
Change-Id: I5686deb0ae4f9927192a039d08adc0117b2605dd
diff --git a/java/droiddoc.go b/java/droiddoc.go
index 3b7ead5..9821bcf 100644
--- a/java/droiddoc.go
+++ b/java/droiddoc.go
@@ -540,20 +540,13 @@
 	var bootClasspathArgs, classpathArgs string
 
 	javaVersion := getJavaVersion(ctx, String(j.properties.Java_version), String(j.properties.Sdk_version))
-	if javaVersion == "1.9" || ctx.Config().UseOpenJDK9() {
-		if len(deps.bootClasspath) > 0 {
-			var systemModules classpath
-			if deps.systemModules != nil {
-				systemModules = append(systemModules, deps.systemModules)
-			}
-			bootClasspathArgs = systemModules.FormJavaSystemModulesPath("--system ", ctx.Device())
-			bootClasspathArgs = bootClasspathArgs + " --patch-module java.base=."
+	if len(deps.bootClasspath) > 0 {
+		var systemModules classpath
+		if deps.systemModules != nil {
+			systemModules = append(systemModules, deps.systemModules)
 		}
-	} else {
-		if len(deps.bootClasspath.Strings()) > 0 {
-			// For OpenJDK 8 we can use -bootclasspath to define the core libraries code.
-			bootClasspathArgs = deps.bootClasspath.FormJavaClassPath("-bootclasspath")
-		}
+		bootClasspathArgs = systemModules.FormJavaSystemModulesPath("--system ", ctx.Device())
+		bootClasspathArgs = bootClasspathArgs + " --patch-module java.base=."
 	}
 	if len(deps.classpath.Strings()) > 0 {
 		classpathArgs = "-classpath " + strings.Join(deps.classpath.Strings(), ":")