ls: avoid expensive capability lookup by default

ls: avoid expensive capability lookup by default

Lookup of file-based capabilities adds 30% overhead to the common
case of ls --color usage.  Since the use of file capabilities is
very rare, it doesn't make sense to pay this cost in the common
case.  It's better to use getcap to inspect capabilities, and the
following run shows only 8 files using capabilities on my fedora
35 distro (14 years after the feature was introduced to the linux
kernel).

  $ getcap -r /
  /usr/bin/arping = cap_net_raw+p
  /usr/bin/clockdiff = cap_net_raw+p
  /usr/bin/gnome-keyring-daemon = cap_ipc_lock+ep
  /usr/bin/gnome-shell = cap_sys_nice+ep
  /usr/bin/newgidmap = cap_setgid+ep
  /usr/bin/newuidmap = cap_setuid+ep
  /usr/sbin/mtr-packet = cap_net_raw+ep
  /usr/sbin/suexec = cap_setgid,cap_setuid+ep

* src/dircolors.hin: Set "CAPABILITY" to "00", to indicate unused.
* src/ls.c: Set the default C_CAP color to not colored.
* NEWS: Mention the change in behavior.