Stop managing one more mediawiki git submodule

The mediwiki vendor repo is managed as a submodule and is already
checked out for us. We don't need to manage it directly with vcsrepo.
Doing so fails as the dir exists and isn't a full git repo.

Change-Id: Ibd74f66a90ea4300e27a0e5a14c58f0c209563a5

manifests/app.pp

@@ -7,13 +7,6 @@ class mediawiki::app ($revision = 'origin/REL1_27'){
     source   => 'https://gerrit.wikimedia.org/r/mediawiki/core.git',
     revision => $revision,
   }
-  vcsrepo { '/srv/mediawiki/w/vendor':
-    ensure   => present,
-    provider => git,
-    source   => 'https://gerrit.wikimedia.org/r/mediawiki/vendor.git',
-    revision => $revision,
-    require  => Vcsrepo['/srv/mediawiki/w'],
-  }
   file { '/srv/mediawiki/w/cache':
     ensure  => directory,
     recurse => true,