mt76: firmware: Double firmware cleanup

Firmware files:

• mt7986_eeprom_mt7975_dual.bin
• mt7986_eeprom_mt7976.bin
• mt7986_eeprom_mt7976_dbdc.bin
• mt7986_eeprom_mt7976_dual.bin

are in same versions as in mt76.

Below firmware files (coming from MTK SDK) are newer than those from mt76 tarball. Agreed to use firmware files coming with mt76 as those are considered compatible. Checked that even if firmware files are available in openwrt_core package, those from mt76 tarball are finally taken into build.

• mt7986_rom_patch.bin (20220113162543a vs 20221012200311a)
• mt7986_rom_patch_mt7975.bin (20220113162701a vs 20221012200311a)
• mt7986_wa.bin (00000020220113163034 vs 00000020221012200338)
• mt7986_wm.bin (00000020220113162641 vs 00000020221012200339)
• mt7986_wm_mt7975.bin (00000020220113162756 vs 00000020221012200339)

Below firmware files are not available in current mt76 tarball, so are not removed:

• mt7986_eeprom_mt7975.bin
• mt7986_wo_0.bin
• mt7986_wo_1.bin