Documentation/features/lib: Remove arch support status file for 'strncasecmp'

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>