feat(types): Remove _type field

Currently, we create numerous elasticsearch types, corresponding to
different layers. All the types are identical, so they don't really
serve any value.

In Elasticsearch 6 [mapping types will go away](https://www.elastic.co/guide/en/elasticsearch/reference/6.2/removal-of-types.html).
The sooner we can remove our minimal usage of types, the easier that
transition will be.

Its possible that this will give us a performance benefit right away,
although it probably won't. It _will_ simplify our code a bit though!

Connects pelias/pelias#719

Document.js

@@ -41,12 +41,6 @@ function Document( source, layer, source_id ){
   this.setLayer( layer );
   this.setSourceId( source_id );
   this.setId( source_id );
-
-  // set the elasticsearch '_type' property to be the same as $layer
-  // this may be removed/modified in the future if required but will mean
-  // that; for example; all 'address' data ends up in the same '_type', even
-  // if it comes from different sources.
-  this.setType( layer );
 }
 
 Document.prototype.toJSON = function(){
@@ -101,8 +95,9 @@ Document.prototype.toESDocument = function() {
 
   return {
     _index: config.schema.indexName,
-    _type: this.getType(),
     _id: this.getId(),
+    // From ES5 onward, the default mapping type name is '_doc'. However ES2 does not allow that, so use 'doc' for now
+    _type: 'doc',
     data: doc
   };
 };
@@ -122,20 +117,6 @@ Document.prototype.getId = function(){
   return this._meta.id;
 };
 
-// type
-Document.prototype.setType = function( type ){
-
-  validate.type('string', type);
-  validate.truthy(type);
-
-  this._meta.type = type;
-  return this;
-};
-
-Document.prototype.getType = function(){
-  return this._meta.type;
-};
-
 // source
 Document.prototype.setSource = function( source ){
 

test/Document.js

@@ -9,9 +9,6 @@ module.exports.tests.interface = function(test) {
     t.equal(typeof Document.prototype.getId, 'function', 'getId() is a function');
     t.equal(typeof Document.prototype.setId, 'function', 'setId() is a function');
 
-    t.equal(typeof Document.prototype.getType, 'function', 'getType() is a function');
-    t.equal(typeof Document.prototype.setType, 'function', 'setType() is a function');
-
     t.equal(typeof Document.prototype.getSource, 'function', 'getSource() is a function');
     t.equal(typeof Document.prototype.setSource, 'function', 'setSource() is a function');
 
@@ -42,7 +39,6 @@ module.exports.tests.constructor = function(test) {
     t.equal(doc.layer, 'mylayer', 'setter called');
     t.equal(doc.source_id, 'myid', 'setter called');
     t.equal(doc._meta.id, 'myid', 'setter called');
-    t.equal(doc._meta.type, 'mylayer', 'setter called');
 
     t.end();
   });

test/document/toESDocument.js

@@ -46,8 +46,8 @@ module.exports.tests.toESDocument = function(test) {
 
     var expected = {
       _index: 'pelias',
-      _type: 'mylayer',
       _id: 'myid',
+      _type: 'doc',
       data: {
         layer: 'mylayer',
         name: {
@@ -94,8 +94,8 @@ module.exports.tests.toESDocument = function(test) {
 
     var expected = {
       _index: 'pelias',
-      _type: 'mylayer',
       _id: 'myid',
+      _type: 'doc',
       data: {
         source: 'mysource',
         layer: 'mylayer',

test/run.js

@@ -14,7 +14,6 @@ var tests = [
   require('./document/address.js'),
   require('./document/parent.js'),
   require('./document/polygon.js'),
-  require('./document/type.js'),
   require('./document/category.js'),
   require('./document/boundingbox.js'),
   require('./document/source.js'),

test/serialize/test.js

@@ -19,7 +19,6 @@ module.exports.tests.minimal = function(test) {
     var s = serializeDeserialize( doc );
 
     // document meta data
-    t.equal(doc.getMeta('type'), 'mylayer', 'correct _meta');
     t.equal(doc.getMeta('id'), 'myid', 'correct _id');
 
     // document body
@@ -64,7 +63,6 @@ module.exports.tests.complete = function(test) {
     var s = serializeDeserialize( doc );
 
     // document meta data
-    t.equal(doc.getMeta('type'), 'venue', 'correct _meta');
     t.equal(doc.getMeta('id'), '1003', 'correct _id');
 
     // document body