This reverts commit c92b4b54be.
Pure GPT would be nice, but older EEPROM/firmware version seem not to
handle it properly (before EEPROM 2020-09-03/firmware 2020-10-22). Since
devices still get shipped with older EEPROM we currently moving to pure
GPT would make those devices not booting.
Stick with hybrid mode for now to make sure HAOS boots on all devices no
matter if a new or old EEPROM is in use.
