scout: Fix a lot of dead assignments

In lots of places scout takes the return value of a graphics
function, then decides it doesn't actually care about the result.

Get rid of the assignments, as they provide a false sense of
security.

Caught by clang-analyzer

Change-Id: I1ea8514b969777f1276b4e8f8ab946a4d36a870c
Reviewed-on: http://gerrit.openafs.org/9238
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>