chromium: Fix desktop icon and duplicate entry.

This should fix the desktop icon location for both desktop entries (the
one from the Chromium derivation itself and the wrapper) and renames the
name of the file so that it gets overridden by the wrappers desktop item
so we don't end up having two of them.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
(cherry picked from commit d8f8f317269d74e7e201051e77e16f7533d1e4b6)
Signed-off-by: aszlig <aszlig@redmoonstudios.org>