BUG: drop link checking with htmlproofer but allow it to check alt tags and other accessibility things?

[lwasser]

i wonder if we can turn off link checking for html proofer and just use it for alt tags. @willingc what do you think? my latest pr and all of @kierisi fail because it's a new page on the site that doesn't exist yet. lychee seems to be doing the job for us. could we just setup htmlproofer to not check links (if that is an option?.

thoughts?

[willingc]

I'm fine with removing htmlproofer and replacing the accessibility checks in another way.