Remove extra establish connection in pending migrations

`purge` always re-establishes the connection at the end so we _should_
always have a connection and shouldn't need to re-establish.

activerecord/lib/active_record/migration.rb

@@ -638,7 +638,6 @@ def check_pending!(connection = Base.connection)
       end
 
       def load_schema_if_pending!
-        current_db_config = Base.connection_db_config
         all_configs = db_configs_in_current_env
 
         needs_update = !all_configs.all? do |db_config|
@@ -654,9 +653,6 @@ def load_schema_if_pending!
           end
         end
 
-        # Establish a new connection, the old database may be gone (db:test:prepare uses purge)
-        Base.establish_connection(current_db_config)
-
         check_pending_migrations(db_configs: all_configs)
       end