[Tails-dev] [review'n'merge] remove alt text

Hello, sometimes in the website, the alt tag of images is used as a
title or as a description instead of a text replacement for the image
content.
For some of them I remove the alt text, when no text replacement is
required.

Please review and merge.

Repo: https://git-tails.immerda.ch/xin/tails/
Branch: remove_alt_text
Last Commit: 962723428ddc37faf2253fea578610a1ce8dc2cc

Cheers.
xin