docs: un-deprecate kill(1)

docs: un-deprecate kill(1)

 * util-linux kill implementation is used in many distributions

 * the latest active procps upstream (fork at http://gitorious.org/procps/)
   does not build kill(1) by default

 * util-linux implementation is actively improved and we follow Linux
   kernel features (e.g. RT signals, sigqueue(2) support, ...)

 * kill(1) is basic command without dependence on /proc, it does not make
   sense to have it in procps package.

... so it does not make sense to mark deprecate this code.

Signed-off-by: Karel Zak <kzak@redhat.com>