Use packaged unminimize in the ubuntu-server images

unminimize is currently present at /usr/local/sbin/unminimize,
which is spit out by livecd-rootfs currently. We'd like to switch
that to use the packaged unminimize, which will be at
/usr/bin/unminimize instead.

(cherry picked from commit 7535bf7bc7)

live-build/ubuntu-server/hooks/01-unminimize.chroot_early

@@ -12,7 +12,7 @@ esac
 
 # Run the unminimize script to re-install packages with all dpkg filters removed and install packages
 # removed as part of minimization
-yes | /usr/local/sbin/unminimize
+yes | /usr/bin/unminimize
 
 # Fix up missing recommends.  Other non-layered flavors handle this in
 # live-build/auto/build, but we need to do it here.  Also, there are