Use Mastondon social media link for verification too

[chalin]

Once Docsy supports the following:

• https://github.com/google/docsy/issues/1380

The drop the separate Mastondon site verification link in the homepage (#2216) in favor of using the social media link that appears in the footer (note that it's configured via the Hugo config file).

This is a followup to #2104.

[kennykguo]

if this issue is still active, please assign this issue to me, thanks

[svrnm]

@kennykguo this issue is not assignable as per the description it has a dependency on a docsy issue. Please note that we are not assigning issues, as per our contribution guidelines