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
Merge "Drop dead code from all SVG source files"