RFC: Remove direct-boot support

[SergioGasquez]

Since it was removed in esp-hal, shall we remove direct-boot support?

[MabezDev]

Imo there doesn't seem to be a maintenance cost in keeping it, and it still might be useful for other frameworks, for example Zephyr recently started supporting it (though they called it simple boot). With that said, I don't maintain espflash so I will leave the decision to someone more qualified :D.

[SergioGasquez]

I guess we can leave it, the RFC idea was linked to #519 (comment), and we've decided to keep ESP8266, so lets go with the same approach here.