Remove conversation URI (#11423)

It is not part of ActivityPub and will free up a lot of space

db/post_migrate/20190519130537_remove_boosts_widening_audience.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class RemoveBoostsWideningAudience < ActiveRecord::Migration[5.2]
   disable_ddl_transaction!
 

db/post_migrate/20190728084117_remove_uri_from_conversations.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class RemoveUriFromConversations < ActiveRecord::Migration[5.2]
+  def up
+    safety_assured { remove_column :conversations, :uri, :string }
+  end
+
+  def down
+    add_column :conversations, :uri, :string
+    add_index :conversations, :uri, unique: true
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2019_07_26_175042) do
+ActiveRecord::Schema.define(version: 2019_07_28_084117) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -203,10 +203,8 @@ ActiveRecord::Schema.define(version: 2019_07_26_175042) do
   end
 
   create_table "conversations", force: :cascade do |t|
-    t.string "uri"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.index ["uri"], name: "index_conversations_on_uri", unique: true
   end
 
   create_table "custom_emoji_categories", force: :cascade do |t|