Is your feature request related to a problem? Please describe.

SAPI4 is no longer maintained or supported. It is known to rely on libraries that pose a security risk. In #17599 SAPI4 was deprecated, and a message added to warn users of its pending removal.

Describe the solution you'd like

Remove synthDrivers.sapi4 and synthDrivers._sapi4. Remove mentions of SAPI4 from the user guide.

Describe alternatives you've considered

Keep the SAPI4 code. It only makes vulnerable calls if in use, so poses little risk to most users.

Additional context