remove code to migrate legacy cookies

we've verified that the legacy cookies are not in use anymore, hence we can get rid of this migration logic to simplify the client side code.

here's a link to the same change we made on the server (internal link) https://github.com/segmentio/xid/pull/12.

Author: f2prateek

lib/index.js

@@ -169,16 +169,6 @@ Segment.prototype.initialize = function() {
     self.ready();
   });
 
-  // Migrate from old cross domain id cookie names
-  if (this.cookie('segment_cross_domain_id')) {
-    this.cookie('seg_xid', this.cookie('segment_cross_domain_id'));
-    this.cookie('seg_xid_fd', this.cookie('segment_cross_domain_id_from_domain'));
-    this.cookie('seg_xid_ts', this.cookie('segment_cross_domain_id_timestamp'));
-    this.cookie('segment_cross_domain_id', null);
-    this.cookie('segment_cross_domain_id_from_domain', null);
-    this.cookie('segment_cross_domain_id_timestamp', null);
-  }
-
   // Delete cross domain identifiers.
   this.deleteCrossDomainIdIfNeeded();
 

test/index.test.js

@@ -883,14 +883,6 @@ describe('Segment.io', function() {
             server.restore();
           });
 
-          it('should migrate cookies from old to new name', function() {
-            segment.cookie('segment_cross_domain_id', 'xid-test-1');
-            segment.initialize();
-
-            analytics.assert(segment.cookie('segment_cross_domain_id') == null);
-            analytics.assert(segment.cookie('seg_xid') === 'xid-test-1');
-          });
-
           it('should not crash with invalid config', function() {
             segment.options.crossDomainIdServers = undefined;