Since it was introduced in 5ce0db9f43,
we've had alt text for the hotspots illustration with an invalid
translation tag.
Fix this by removing the alt text, since the image has no functional
effect and so the right answer should it fail to load or the user is
visually impaired is to ignore it.
This reverses the policy that was set, but incompletely enforced, by
commit 951514dd7d. The self-closing tag
syntax is clearer, more consistent, simpler to parse, compatible with
XML, preferred by Prettier, and (most importantly now) required by
FormatJS.
Signed-off-by: Anders Kaseorg <anders@zulip.com>