firmware: delete in-kernel firmware

firmware: delete in-kernel firmware

The last firmware change for the in-kernel firmware source code was back
in 2013.  Everyone has been relying on the out-of-tree linux-firmware
package for a long long time.

So let's drop it, it's baggage we don't need to keep dragging around
(and having to fix random kbuild issues over time...)

Cc: Kyle McMartin <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Michal Marek <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Acked-by: David Woodhouse <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>