Well, after months of working on other things, I inadvertently stumbled upon a work-around that removed the field name from the legend. I'm now using version 3.16.
I set the attributeField property of the ClassBreaksRenderer to a function (instead of just giving it the name of a field).
So, the line of code that creates my ClassBreaksRenderer is:
flyrRenderer = new CBRenderer(null, rendfunc0);
And the function that determines the values (located just above the renderer-creating line) is:
rendfunc0 = function(feature) {
var value = (feature.attributes)[field];
return value;
}
I kept everything else the same - setting class breaks, symbols, etc. And now there is no field name showing up in the legend.
This accomplishes the task I was setting out to do... There may be a better answer out there (perhaps in JS API 4?).