mediatek: fix eeprom loading (Mercusys MR90X v1)

mediatek: fix eeprom loading (Mercusys MR90X v1)

Commit mt76: drop default eeprom file for mt7986-firmware
(e3aa645b267ca4f08773b5366583e9b0020fc3e9) breaks eeprom loading for
Mercusys MR90X v1. As a result WiFi is not working at all.

This commit adds Mercusus MR90x to the caldata script (it works after the
commit mentioned above). And we can safely drop "81_fix_eeprom" script
as it's no longer required.

Fixes: e3aa645b267ca4f08773b5366583e9b0020fc3e9
Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>