Remove useless material from DAW's mathbox
Remove useless material from DAW's mathbox

This commit removes some material from my (DAW) mathbox that,
on further reflection, I think is useless / superceded.
Nothing else depends on this.

Signed-off-by: David A. Wheeler <9ae72d22d8b894b865a7a496af4fab6320e6abb2@dwheeler.com>

metamath/set.mm,metamath/set.mm,metamath/set.mm