Link reporter should ignore anchor links

www.agileplannerapp.com/boards/173808/cards/6121

Anchor links link to content within the page,
hence we should not report them as broken.
Data migration to remove anchor links

Anchor links should never have been part of
broken link reports, because they link to
sections on the same page.
Merge pull request #1792 from alphagov/fix-broken-link-reporter

Link reporter should ignore anchor links