Revert "cpuset: add --count"

The patch introduced a behavior change coming from getopt_long, namely
the entire argument array would be parsed looking for opts, which
affected uses spawning new processes without passing '--' to delimit
where cpuset arguments end. [1]

Apart from that turns out the change had a bug: using CPU_LEVEL_ROOT
instead of CPU_LEVEL_WHICH, returning a different cpuset than intended.
[2]

The intended functionality is provided with nproc(1), which landed after
this change.

As such, revert for the time being.

This reverts commit d9d5f2c042a51a9f0dd69eb1fc349efd81ffa483.

Reported by: Mark Millard [1]
Reported by: jbeich [2]