fix #4136 - don't draw ticks corresponding to _linepositions

... when mirror isn't 'allticks' as _linepositions gets
    filled in lsInner (in subroutines.js) when mirror is set
    to 'all' OR 'allticks'

Author: etpinard

src/plots/cartesian/axes.js

@@ -1759,7 +1759,9 @@ axes.drawOne = function(gd, ax, opts) {
             transFn: transFn
         });
 
-        tickSubplots = Object.keys(ax._linepositions || {});
+        if(ax.mirror === 'allticks') {
+            tickSubplots = Object.keys(ax._linepositions || {});
+        }
     }
 
     for(i = 0; i < tickSubplots.length; i++) {