Bug 36845: Exclude meta tag from the translations

Bug 36845: Exclude meta tag from the translations

This bug originaly wants to get rid of "noindex" coming from this meta
tag:
  <meta name="robots" content="noindex">

But actually we have other strings from the meta tags that should not be
translated.

Test plan:
0. Do not apply this patch
1. cd misc/translator/po && gulp po:update --lang es-ES (or any other
   lang)
2. git commit -a -m"wip"
3. Apply this patch
4. Repeat 1 and git diff to show the diff
Notice that strings that should not be translated are removed from the
po files (actually commented)

Signed-off-by: Caroline Cyr La Rose <caroline.cyr-la-rose@inlibro.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit fbb123b12eab123e62c508944fd2b6261fb24acf)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>