remove setScale categories fallback and update heatmap test comment

Author: alexcjohnson

src/plots/cartesian/set_convert.js

@@ -419,11 +419,6 @@ module.exports = function setConvert(ax, fullLayout) {
     ax.setScale = function(usePrivateRange) {
         var gs = fullLayout._size;
 
-        // TODO cleaner way to handle this case
-        if(!ax._categories) ax._categories = [];
-        // Add a map to optimize the performance of category collection
-        if(!ax._categoriesMap) ax._categoriesMap = {};
-
         // make sure we have a domain (pull it in from the axis
         // this one is overlaying if necessary)
         if(ax.overlaying) {

test/jasmine/tests/heatmap_test.js

@@ -298,8 +298,10 @@ describe('heatmap calc', function() {
 
         fullTrace._extremes = {};
 
-        // clearCalc used to be (oddly enough) part of supplyDefaults.
-        // Now it's in doCalcData, which we don't include in this partial pathway.
+        // we used to call ax.setScale during supplyDefaults, and this had a
+        // fallback to provide _categories and _categoriesMap. Now neither of
+        // those is true... anyway the right way to do this though is
+        // ax.clearCalc.
         fullLayout.xaxis.clearCalc();
         fullLayout.yaxis.clearCalc();