Fix ZCML conflicts

Remove p.a.contentlisting ZCML registration since collective.solr>=3.1 does this now.

ftw.solr is not bootable currently:
```
ConfigurationConflictError: Conflicting configuration actions
  For: ('adapter', (<class 'collective.solr.parser.SolrResponse'>,), <InterfaceClass plone.app.contentlisting.interfaces.IContentListing>, '')
    File "/Users/jone/projects/packages/ftw.solr/ftw/solr/configure.zcml", line 23.4-25.52
          <adapter
              factory="plone.app.contentlisting.contentlisting.ContentListing"
              for="collective.solr.parser.SolrResponse" />
    File "/Users/jone/projects/python/cache/eggs/collective.solr-3.1-py2.7.egg/collective/solr/configure.zcml", line 80.2-84.8
        <adapter
            zcml:condition="installed plone.app.contentlisting"
            factory="plone.app.contentlisting.contentlisting.ContentListing"
            for="collective.solr.parser.SolrResponse"
            />
  For: ('adapter', (<class 'collective.solr.flare.PloneFlare'>,), <InterfaceClass plone.app.contentlisting.interfaces.IContentListingObject>, '')
    File "/Users/jone/projects/packages/ftw.solr/ftw/solr/configure.zcml", line 26.4-28.49
          <adapter
              factory="ftw.solr.contentlisting.SolrContentListingObject"
              for="collective.solr.flare.PloneFlare" />
    File "/Users/jone/projects/python/cache/eggs/collective.solr-3.1-py2.7.egg/collective/solr/configure.zcml", line 86.2-90.8
        <adapter
            zcml:condition="installed plone.app.contentlisting"
            factory="collective.solr.contentlisting.FlareContentListingObject"
            for="collective.solr.flare.PloneFlare"
            />
```

/cc @maethu @buchi @lukasgraf