The debugger has fallen behind and has become a maintenance burden. It was
the only user of the old kernel US layout system, which is good to get rid
of. The debugger didn't work with graphical output and was likely to
conflict with the new keyboard system if used, which no longer triggered it.
The kernel symbol code was removed to simplify the kernel.
The kernel debugger was an useful debugging feature, but it needs to be done
in a better way before it can be added back.
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