console: mdacon: remove this obsolete driver

console: mdacon: remove this obsolete driver

The mdacon driver supports using ISA MDA or Hercules-compatible display
adapters as a secondary text console. This was commonly used in the
1990s and earlier for debugging software which took over the primary
display. It is highly unlikely anyone is doing so nowadays because
serial consoles and much better methods of debugging exist.

The driver is not enabled by any defconfig, nor any of the
dozens of distro configs collected at [1]. It has been relegated to VTs
13-16 since commit 0b9cf3aa6b1e ("mdacon messing up default vc's - set
default to vc13-16 again") in Linux 2.6.27 (and before Linux 2.5.53 -
see the link in the message of the above commit). The change in 2.6.27
was done because it was incorrectly detecting non-MDA adapters as MDA
and taking over all VTs, rendering them unusable.

Furthermore, vgacon supports using MDA/Hercules-compatible adapters as
the primary text console, so any systems with only one of these
adapters were already using vgacon and will not experience any loss in
functionality from the removal of this driver.

Given all of these factors, the mdacon driver is likely entirely
unused. Remove it.

[1] https://github.com/nyrahul/linux-kernel-configs/tree/f0bee86a135a0406ea427855f52702dd00d770f9

Signed-off-by: Ethan Nelson-Moore <enelsonmoore@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>