DROP FUNCTION collection_timestamp(uid VARCHAR, resource VARCHAR) doesn't exists

kinto.core.storage.exceptions.BackendError: ProgrammingError: (psycopg2.errors.UndefinedFunction) function collection_timestamp(character varying, character varying) does not exist

When running the migrations between kinto 12 to kinto 13, this error message can happen. We should ignore the deletion if the function does not exists.

Start by locating the migration that runs when upgrading from Kinto 12 to Kinto 13 and reproducing the reported psycopg2 UndefinedFunction error for collection_timestamp(uid VARCHAR, resource VARCHAR). The migration is done when deletion succeeds both with and without that function present.

Written by the indexing model from the issue text.