fix loplugin:unusedmethods

revert the part of
    commit 9f4d23c1
    Date:   Mon Aug 13 17:24:26 2018 +0200
    filter out some of the AST in the plugins
that applied to this plugin. Turns out it really needs to see __all__
the code in order to produce good results.

Change-Id: If580a701049d2570f2a833327b2189641090079b
Reviewed-on: https://gerrit.libreoffice.org/60279Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>

compilerplugins/clang/unusedmethods.cxx

@@ -75,11 +75,11 @@ static std::set<MyFuncInfo> calledFromOutsideSet;
 
 
 class UnusedMethods:
-    public loplugin::FilteringPlugin<UnusedMethods>
+    public RecursiveASTVisitor<UnusedMethods>, public loplugin::Plugin
 {
 public:
     explicit UnusedMethods(loplugin::InstantiationData const & data):
-        FilteringPlugin(data) {}
+        Plugin(data) {}
 
     virtual void run() override
     {