Bug 17639 - Remove white filling inside of Koha logo

Bug 17639 - Remove white filling inside of Koha logo

This patch modifies the Koha logo SVG file to remove the fill from two
letters. This patch also optimizes the file and converts the text object
to paths for better cross-platform portability.

To test you could:

- Open the file in an editor and confirm that the change is correct
  - or -
- Open the file in a browser and use the code inspector to add a
  background-color attribute to the top-level <svg> tag. The logo should
  appear transparent, with no white fills.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>