Remove the volto-plotlycharts add-on from Volto

[charlesons]

Remove the volto-plotlycharts add-on for the following reasons:

• No longer needed as volto-chart-builder provides charting functionality
• Avoid potential confusion for users over which chart block type to select
• Decrease bundle size

Definition of done:

• [x] References to volto-plotlycharts removed from code
• [x] Plotly charts block option no longer appears in the UI

Acceptance criteria:

• [x] Climate-1 site continues to function correctly

[nosnickid]

The deploy for this failed https://ci.ukstats.dev/job/GSS_data/job/dd-cms/job/staging/31/console

I'll take a look into why