configure: build sulogin, watchdogd, and libsystemd by default

v5.0 ships keventd and the D-Bus support enabled out of the box, but the
remaining bundled pieces stayed opt-in, and the help text for two of them
already claimed otherwise.

Default all three to yes; --without-sulogin, --without-watchdog, and
--without-libsystemd opt out.  The distcheck and CI configure lines drop
the flags they no longer need, so CI exercises the defaults.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Makefile.am

@@ -63,7 +63,6 @@ release: distcheck
 		printf "$$file.sha256\t"; cat ../$$file.sha256 | cut -f1 -d' ';	\
 	done
 
-DISTCHECK_CONFIGURE_FLAGS = --prefix=/usr --sysconfdir=/etc --localstatedir=/var   \
-			    --enable-testserv-plugin --enable-x11-common-plugin    \
-			    --with-watchdog --with-keventd --with-fstab=/etc/fstab \
-			    --with-libsystemd --with-bash-completion-dir=no
+DISTCHECK_CONFIGURE_FLAGS = --prefix=/usr --sysconfdir=/etc --localstatedir=/var \
+			    --enable-testserv-plugin --enable-x11-common-plugin  \
+			    --with-fstab=/etc/fstab --with-bash-completion-dir=no