mflash: Remove this broken flash driver

mflash: Remove this broken flash driver

This is causing repeated build failures. Its design is so fundamentally
broken that if someone actually wants to use it, a full rewrite is the
only option. So it's not even worth deprecating in the hope that someone
will notice and fix it, just get rid of it.

Change-Id: I513069919a3873bd69253110f7fb6f622ee7d061
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/5243
Tested-by: jenkins
Reviewed-by: Jeffrey Booher-Kaeding <Jeff.Booher-Kaeding@arm.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>