man4: remove references to gone eeprom(8) and obsolete devices

The former was missed in 702547720ca01437081fb1b6f9eb281c9541021b and
r357794 respectively.
Additionally for dc.4 and gem.4, remove on-board and SBus devices whose
support was removed as part of 58aa35d42975c298ca0adba705c042596303c9f5
and r357455 respectively.