build.7: Improve make delete-old example

Be more explicit that deleting old files and libraries needs to be
really after you're rebooted a third time and you're really actually
sure your applications aren't using old libs, following irc discussion.

Also adjust an example slightly to fit on 80 character console.

MFC after:		3 days
Discussed with:		emaste, fuz, jhb
Differential Revision:	https://reviews.freebsd.org/D54079

share/man/man7/build.7

@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd September 25, 2025
+.Dd April 6, 2026
 .Dt BUILD 7
 .Os
 .Sh NAME
@@ -1018,16 +1018,20 @@ shutdown -r now
 .Pp
 For major version upgrades, boot into single-user mode.
 After restarting, install userspace, and merge configurations.
-After verifying that you do not need them, delete old files
-and libraries:
+After verifying that you do not need them, delete old files:
 .Bd -literal -offset indent
 cd /usr/src
 etcupdate -p
 make installworld
 etcupdate -B
-make delete-old delete-old-libs
+make delete-old
 shutdown -r now
 .Ed
+.Pp
+After testing the new system and verifying that your applications do not
+depend on them, delete the old libraries:
+.Pp
+.Dl make delete-old-libs
 .Ss Example 2: Build and upgrade a custom kernel in place
 Create a custom kernel configuration,
 .Va MYKERNEL ,
@@ -1103,21 +1107,21 @@ such as amd64:
 .Bd -literal -offset indent
 cd /usr/src
 make TARGET_ARCH=aarch64 buildworld buildkernel
-make TARGET_ARCH=aarch64 DESTDIR=/armclient installworld installkernel
+make TARGET_ARCH=aarch64 DESTDIR=/client installworld installkernel
 .Ed
 .Pp
 Afterwards, to build and install a single piece of userspace, use:
 .Bd -literal -offset indent
 cd src/bin/ls
 make buildenv TARGET_ARCH=aarch64
-make clean all install DESTDIR=/armclient
+make clean all install DESTDIR=/client
 .Ed
 .Pp
 Likewise, to quickly rebuild and reinstall the kernel, use:
 .Bd -literal -offset indent
 cd src
 make buildenv TARGET_ARCH=aarch64
-make kernel KERNFAST=1 DESTDIR=/armclient
+make kernel KERNFAST=1 DESTDIR=/client
 .Ed
 .Sh DIAGNOSTICS
 .Bl -diag