remove cpu_exclusive and mem_exclusive options

[Vinjar Hillestad]

The options for the "cset" subcommand "set", "--mem_exclusive" and "--cpu_exclusive"
are implemented as options in the program, help output and documented in the man page.

The functionality is however not implemented.

-----------
$ cset set -l

cset:
         Name CPUs-X MEMs-X Tasks Subs Path
 ------------ ---------- - ------- - ----- ---- ----------
         root 0-3 y 0 y 0 1 /
       docker 0-3 n 0 n 0 1 /docker
$ cset set --mem_exclusive root
cset: Modification of cpu_exclusive and mem_exclusive not implemented.

$ cset set --cpu_exclusive root
cset: Modification of cpu_exclusive and mem_exclusive not implemented.
-----------

This seems to be the case for the xenial, bionic and focal version of this package.

I realize this might not be a bug, but the package makes promises it can't deliver on.