removed citation_type from repository metadata

-all internal citations are NOMAD DOIs which are stored separately, thus only
 external citations are stored as citations in ElasticSearch

meta_info/nomad_meta_info/repository.nomadmetainfo.json

@@ -39,13 +39,6 @@
       "superNames": [
         "section_citation"
       ]
-    }, {
-      "description": "The type of citation (internal or external)",
-      "dtypeStr": "C",
-      "name": "citation_type",
-      "superNames": [
-        "section_citation"
-      ]
     }, {
       "description": "String defining the citation",
       "dtypeStr": "C",