Update references from "1.9" to "9"

This is a follow-up pass for JDK-8136494 and JDK-8149601 which updated "@since 1.9" to "@since 9" to match java.specification.version.

The following files contain references to "1.9" which should be updated to "9":

jdk:

src/java.desktop/macosx/classes/com/apple/eawt/Application.java

langtools:

src/jdk.compiler/share/classes/com/sun/source/doctree/HiddenTree.java