vmimage.subr: pkg autoremove after pkg install

A bug in pkg, which somehow only surfaced as a consequence of pkgbase,
results in pkg install sometimes pulling in false dependencies.  This
problem might be limited to cases when the lib32 pkgbase packages are
not installed.  In the case of EC2 "small" images, installing the
ebsnvme-id package results in binutils, gcc12-devel, gmp, indexinfo,
liblz4, mpc, mpfr, and zstd packages being installed.

These false dependencies are however not recorded as dependencies --
at some level pkg does understand that they're not needed -- so running
pkg autoremove immediately after pkg install cleans them up.

Note: This does not remove lines from METALOG corresponding to these
packages, and makefs emits an error when it attempts to create the
filesystem but cannot find the files listed in METALOG -- but makefs
does seem to complete normally despite the error messages.

This change should be reverted once the pkg issue has been located and
fixed.

Reviewed by:	ivy
MFC after:	3 days
Sponsored by:	https://www.patreon.com/cperciva
Differential Revision:	https://reviews.freebsd.org/D53543

release/tools/vmimage.subr

@@ -212,6 +212,13 @@ vm_extra_install_packages() {
 			    -r ${DESTDIR} \
 			    install -y -r ${PKG_REPO_NAME} $pkg
 		done
+		INSTALL_AS_USER=yes \
+		${PKG_CMD} \
+		    -o ABI=${PKG_ABI} \
+		    -o REPOS_DIR=${PKG_REPOS_DIR} \
+		    -o PKG_DBDIR=${DESTDIR}/var/db/pkg \
+		    -r ${DESTDIR} \
+		    autoremove
 		metalog_add_data ./var/db/pkg/local.sqlite
 	else
 		if [ -n "${WITHOUT_QEMU}" ]; then
@@ -224,6 +231,8 @@ vm_extra_install_packages() {
 			chroot ${DESTDIR} ${EMULATOR} env ASSUME_ALWAYS_YES=yes \
 				/usr/sbin/pkg install -y ${p}
 		done
+		chroot ${DESTDIR} ${EMULATOR} env ASSUME_ALWAYS_YES=yes \
+		    /usr/sbin/pkg autoremove
 	fi
 
 	return 0