Optimize all SVGs

Once more, with feeling. First reverted attempt: a9b855ee.

Passed with svgo 0.4.2 <https://github.com/svg/svgo>, then prepended
'<?xml version="1.0" encoding="UTF-8"?>' prolog to each file since
svgo sees it fit to remove it and that breaks just about everything.

Previous attempt used a '<?xml version="1.0" ?>' prolog, which
apparently is too short to ensure the file is picked up as an SVG in
some versions of the 'file' utility; see PleaseStand's comments on
bug 59234. We could just add some spaces instead of 'encoding="UTF-8"',
but it seems like a reasonable thing to add.

Skipped the ones in tests/, there's some weird stuff there and they
didn't shrink much when I tried anyway.

Total file size reduced from ~30 KB to ~10 KB.

---

For future reference, the prolog appending was done with the following
script:

for i in `find . -name '*.svg'`
do
    mv $i $i-tmp
    (echo -n '<?xml version="1.0" encoding="UTF-8"?>'; cat $i-tmp) > $i
    rm $i-tmp
done

---

Bug: 59744
Change-Id: Ic9fdd081003b694dbd7e413ca25fffe782b912b5