in all likelyhood if you revoke execute privileges of CTXSYS packages from PUBLIC you will break the Oracle Text feature, check carefully if you don't have any Text indexes.
Officially it is not supported to revoke the default privileges that belong to a product feature, however since a lot of customers want to do this anyway Oracle support
has taken a somewhat more relaxed stance on this topic, the advise being: If you must revoke default privileges from public, it will become your own responsibility
that everything keeps working, this can typically be done by replacing the grants to PUBLIC with some individual grants to (application) schema's that require it.
Please check: note 247093.1 Be Cautious When Revoking Privileges Granted to PUBLIC
Harm ten Napel