rust: use Linux logo

To simplify the Rust patch series and the licensing of the logo,
let's use the Linux logo instead.

For the moment, there is no SVG version, so we use the GIF one.
When the SVG version gets merged [1], we can switch to that one instead.

This allows us to remove from the `rust` branch both the Linux SVG
logo and the Rust for Linux SVG logo, plus the `COPYING-logo` file.

Link: https://lore.kernel.org/lkml/[email protected]/ [1]
Signed-off-by: Miguel Ojeda <[email protected]>

Author: ojeda

Documentation/COPYING-logo

@@ -11,11 +11,3 @@ Larry's web-page:
 
 	https://www.isc.tamu.edu/~lewing/linux/
 
-The SVG version was re-illustrated in vector by Garrett LeSage and
-refined and cleaned up by IFo Hancroft. It is also freely usable
-as long as you acknowledge Larry, Garrett and IFo Hancroft as above.
-
-There are also black-and-white and inverted vector versions at
-Garrett's repository:
-
-	https://github.com/garrett/Tux