Division of MuHash objects are very expensive and multiplication relatively cheap. The whole idea of introducing and tracking numerator and denominators seperately as a representation of the internal state was so that divisions would be rare. So using divison in the Remove method did not make any sense and was just a silly mistake which is corrected here.
This is a partial backport of core#19521
https://github.com/bitcoin/bitcoin/pull/19521/commits/2e2648a9021dfbb6e17dfa81472f057dacbc34e0