packages: Remove the tests-dev package

We don't want a tests-dev package, because this means set-devel depends
on tests-dev, which transitively depends on tests, which means you can't
install set-devel without also getting tests.

The only real "dev" files in tests-dev are from ATF (libprivateatf),
so move that to its own package and add a dependency from tests.

Also move Kyua to its own package, since this might be useful for
running tests even when the user doesn't want the whole set of base
tests installed.

Add a dependency from -tests to both -atf and -kyua, and a dependency
on -set-base, since the tests won't work without the full base system
installed.

The remaining "dev" files in tests are actually test artifacts, not real
development libraries.  Add a new NO_DEV_PACKAGE option to bsd.lib.mk,
which causes dev files to be installed in the base package instead of
creating a -dev package, and set this option for everything that
installs test libraries.

While here, add a slightly more informative description for the tests
package.

MFC after:	3 seconds
Reviewed by:	bapt, emaste
Differential Revision:	https://reviews.freebsd.org/D52597

UPDATING

@@ -27,6 +27,14 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 16.x IS SLOW:
 	world, or to merely disable the most expensive debugging functionality
 	at runtime, run "ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20250918:
+	Kyua has been moved to the FreeBSD-kyua package, and ATF has been moved
+	to the FreeBSD-atf* packages.  If you have FreeBSD-tests installed,
+	these packages will be installed automatically, otherwise you should
+	manually install them if you need these tools.
+
+	This only affects pkgbase users.
+
 20250912:
 	If SRCCONF is unset and a file named src.conf is present at
 	the top of the source tree, it will now be used instead of