refactor herbert_core/utilities/maths/equal_to_tol.m

[cmarooney-stfc]

this routine is commented at L.111-2
% The following code is pretty complex as it has to handle legacy input as
% well. Touch at your peril!
To improve the possibility of maintenance, let's refactor this

[abuts]

I belive, this issue has been resolved as part of the solution for ticket Re #1147