Drop deprecated pointcloud and heatmapgl traces and gl2d subplots

[archmoj]

Closes #7176 and closes #7175.
Users could use scattergl and heatmap traces instead to draw similar graphs.
@plotly/plotly_js

[emilykl]

@archmoj Are scattergl and image direct drop-in replacements for pointcloud and heatmapgl? Or are some of the props different?

Is there a replacement for gl2d subplots?

[emilykl]

LGTM @archmoj , I don't see any red flags as long as tests are passing

[archmoj]

@archmoj Are scattergl and image direct drop-in replacements for pointcloud and heatmapgl? Or are some of the props different?

Is there a replacement for gl2d subplots?

@emilykl No they are not direct drop-in replacements.
gl2d subplots are only only used for these these two traces and other 2-D WebGL-based traces e.g. scattergl, splom and parcoords do not use it.

[archmoj]

@alexcjohnson Would you accept these changes?

[alexcjohnson]

To my understanding it’s actually heatmap that replaces heatmapgl, ie just “downgrading” to the SVG version gives you the same or better performance with many more features. pointcloud is different, scattergl is not a drop-in replacement, but it solves the same use cases and many more.

this is great, I highly support these changes 💃