Staging: comedi: clean up kcomedilib/get.c

Remove all of the unused functions, leaving only those that are
actually called by in-kernel code.

Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>