staging:rtl8192u: Remove unused structure STA_QOS - Style

Remove structure STA_QOS as it is unused in code. This change is a coding
style change so should not impact runtime code execution.

Signed-off-by: John Whitmore <johnfwhitmore@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>