Remove unnecessary index on created_at column on geo_event_log table

db/migrate/20170522201800_create_geo_event_log.rb

@@ -3,7 +3,7 @@ class CreateGeoEventLog < ActiveRecord::Migration
 
   def change
     create_table :geo_event_log, id: :bigserial do |t|
-      t.datetime :created_at, index: true, null: false
+      t.datetime :created_at, null: false
       t.integer :repository_updated_event_id, limit: 8, index: true
 
       t.foreign_key :geo_repository_updated_events,

db/schema.rb

@@ -505,7 +505,6 @@ ActiveRecord::Schema.define(version: 20170602003304) do
     t.integer "repository_updated_event_id", limit: 8
   end
 
-  add_index "geo_event_log", ["created_at"], name: "index_geo_event_log_on_created_at", using: :btree
   add_index "geo_event_log", ["repository_updated_event_id"], name: "index_geo_event_log_on_repository_updated_event_id", using: :btree
 
   create_table "geo_nodes", force: :cascade do |t|