Drop dead code from all SVG source files

Drop dead code from all SVG source files

This matters because these files are actually used as data URI encoded
background images in the CSS.

I did two pretty simple steps:
1. Open each file in Inkscape and save as "normal" SVG. This gets rid
   of most optional stuff but keeps the license information.
2. Open each file in an text/XML editor and delete all unused
   gradients, def sections (if empty) and the Inkscape comment.

I know there are a million ways to do much more agressive compression.
Take this as a first step that - for sure - doesn't break anything.

Bug: 59744
Change-Id: I1bcb2875fe35ca20ee3ad3c648961d4b1c58c0d2