Calendly: Change buttons to a standard link for AMP requests

[Copons]

Once the new Button inner block PR (#15370) is merged we need to use it in Calendly and update it to make it AMP compliant.

See the original PR (#14630 by @pablinos) for more info:

AMP strips out onClick handlers, so when the button version of
the block is rendered we should change it to a standard link to the Calendly
appointment page.

We could probably get around this by attaching the click handler in
another way, but it would still be good to treat an AMP request
differently.

[aaronrobertshaw]

As part of #15863 the Calendly block will render the buttons as links. There is still a little work that needs doing for the AMP requests however. If the Calendly block sets any of the default color styles for the button they'll be missing on AMP views.

[Copons]

As part of #15863 the Calendly block will render the buttons as links. There is still a little work that needs doing for the AMP requests however. If the Calendly block sets any of the default color styles for the button they'll be missing on AMP views.

I think the color issue you are mentioning is the same as this one: #15697
I'm a little unsure on how to tackle it to be honest, but we can at least disregard it in the Calendly (and others) Button replacement PRs.

[Copons]

Fixed by #15863