rm 'fixedrange' from gl3d axis attributes

- this was never implemented
- it was in there *just* to make the call to axisDefaults work

Author: etpinard

src/plots/gl3d/layout/axis_attributes.js

@@ -76,7 +76,6 @@ module.exports = {
     autorange: axesAttrs.autorange,
     rangemode: axesAttrs.rangemode,
     range: axesAttrs.range,
-    fixedrange: axesAttrs.fixedrange,
     // ticks
     tickmode: axesAttrs.tickmode,
     nticks: axesAttrs.nticks,