Staging: panel: remove ifdefs and code for pre-2.6 kernels

The code began 8 years ago with kernel 2.0 or 2.1, and kernels 2.2 and
2.4 were still supported. These old version need no longer be supported
if the code gets merged in mainline.

Signed-off-by: Willy Tarreau <w@1wt.eu>
Cc: Frank Menne <frank.menne@hsm.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>