Flash_erase-nRF52_softdevice_v7.uf2 missing

[hryamzik]

Docs point to the Flash_erase-nRF52_softdevice_v7.uf2 file but it's not in the list of available files to donwload on meshcore.io for Seeed Studio Xiao nRF52 WIO.

[recrof]

fixed by #3282

[hryamzik]

Closing as there's a PR fixing and that PR also covers current flash erase procedure.