If libcap happens to be present in the environment, coreutils will pick it up
and link some applets against it.

Since the idea of coreutils is to provide a full featured alternative to the
busybox applets, do not inhibit the optional dependency but explicitely
require libcap instead.

Fixes the following error spotted on the buildbots:

    Package coreutils-dir is missing dependencies for the following libraries:
    libcap.so.2

Signed-off-by: Jo-Philipp Wich <jo@mein.io>