Rename UpdatableSystemServerJars to ApexSystemServerJars.

This is consistent with naming for boot jars, e.g. ApexBootJars.

Bug: 191127295
Test: presubmit
Change-Id: I6e8828d55ac86b7f5260ed7f8d4eca1c0b3dced8
diff --git a/java/systemserver_classpath_fragment.go b/java/systemserver_classpath_fragment.go
index dfe90ba..6c2a5b5 100644
--- a/java/systemserver_classpath_fragment.go
+++ b/java/systemserver_classpath_fragment.go
@@ -107,7 +107,7 @@
 	global := dexpreopt.GetGlobalConfig(ctx)
 
 	possibleUpdatableModules := gatherPossibleApexModuleNamesAndStems(ctx, s.properties.Contents, systemServerClasspathFragmentContentDepTag)
-	return global.UpdatableSystemServerJars.Filter(possibleUpdatableModules)
+	return global.ApexSystemServerJars.Filter(possibleUpdatableModules)
 }
 
 type systemServerClasspathFragmentContentDependencyTag struct {