tools: 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/

Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Update most userspace consumers of capability.h to use capsicum.h instead.

auditdistd is not updated as I will make the change upstream and then do a
vendor import sometime in the next week or two.

MFC after: 3 weeks

Update existing regression tests after Capsicum overhaul.

Test *at(2) calls with capability-mode lookup.

This commit adds regression testing for openat(), fstatat(), etc. with
capability scoping ("strict relative" lookup), which applies:
- in capability mode
- when performing any *at() lookup relative to a capability

These tests will fail until the *at() code is committed; on my local
instance, with the *at() changes, they all pass.

Approved by: re (kib), mentor (rwatson)
Sponsored by: Google Inc