usr.sbin: Automated cleanup of cdefs and other formatting

Apply the following automated changes to try to eliminate
no-longer-needed sys/cdefs.h includes as well as now-empty
blank lines in a row.

Remove /^#if.*\n#endif.*\n#include\s+<sys/cdefs.h>.*\n/
Remove /\n+#include\s+<sys/cdefs.h>.*\n+#if.*\n#endif.*\n+/
Remove /\n+#if.*\n#endif.*\n+/
Remove /^#if.*\n#endif.*\n/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/types.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/param.h>/
Remove /\n+#include\s+<sys/cdefs.h>\n#include\s+<sys/capsicum.h>/

Sponsored by: Netflix

Remove $FreeBSD$: one-line .c pattern

Remove /^[\s*]*__FBSDID\("\$FreeBSD\$"\);?\s*\n/

yp: Use more accurate function pointer types.

Trim a few duplicate (but incomplete) function prototypes as well.

Reviewed by: zlei, imp
Differential Revision: https://reviews.freebsd.org/D39532

Sync ypwhich(1) code with the OpenBSD version that is more modern.
Update the BSD LICENSE and remove the 3rd clause.

Reviewed by: rodrigc, kib, bapt
Approved by: bapt (mentor)
Obtained from: OpenBSD
Differential Revision: D3249