Truly deprecate the `blackmarket` schema

[Athanasius]

When I was just writing documentation for the blackmarket schema it came to light that this has been 'soft' deprecated since September 2017 !

The same data has been available via the prohibited array defined in the commodity/2 schema since 38076c98bf424f3f50fa5603c8e6a00272934fc4 .

So, properly deprecate this with an announcement of when it will be removed etc.

[Athanasius]

Note:

17:25 Bravada Cadelanne (edgalaxydata) : The last one that wasn't from Elite G19s Companion App was in 2018.