Java: Revert overriding XMLFile.getAPrimaryQlClass()

Library file has to be kept in sync with the other languages, however except
cpp none of them have the getAPrimaryQlClass() predicate declared in a
superclass. Therefore for simplicity revert the change for Java.

java/ql/src/semmle/code/xml/XML.qll

@@ -149,8 +149,6 @@ class XMLFile extends XMLParent, File {
 
   /** Gets a DTD associated with this XML file. */
   XMLDTD getADTD() { xmlDTDs(result, _, _, _, this) }
-
-  override string getAPrimaryQlClass() { result = "XMLFile" }
 }
 
 /**