Remove dynamic social buttons

[rnagle]

See #901.

This PR:

• Removes the dynamic Twitter and Facebook buttons/links from the single post/page template near the byline and replaces them with simple links for the respective share service.
• Removes references to largo_show_twitter_count since it's no longer relevant.
• Updates tests related to largo_post_social_links.

[aschweigert]

does this affect the twitter/fb follow widgets? seems like it might. I'm ok with killing those but some sites are pretty wedded to them, the twitter one, particularly. we'll probably need some kind of plan to deal with that if we do nuke them.

[rnagle]

@aschweigert Yeah, it definitely does affect the twitter and fb widgets. Didn't realize that at first. I added the required scripts back.

Kind of a bummer that we need to load these, but still think we're doing a good thing by not requiring the JS to power the dynamic share buttons.

[benlk]

Do we need the checks for is_single() and is_author() here if the scripts are no longer used as a result of the page being an author or single page?

[benlk]

Tests pass and the buttons work. I have couple questions on the enqueueing made in comments on the diff.

It's a minor issue, but the Print button in the post-header social media buttons doesn't use the 'pointer' cursor used for the other links. This is understandable, because it doesn't have an <a>, but we should probably make it use the pointer cursor instead of a combination of the default arrow for the icon and the text-selection I cursor for the text of the button.