crypto: Make MuHash Remove method efficient

Summary:
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

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11168