[archiso] Remove old code (now redundant)

/etc/mtab symlink is part of [filesystem] since long time

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

archiso/mkarchiso

@@ -265,10 +265,6 @@ _cleanup () {
     fi
     # Delete package pacman related files.
     find "${work_dir}" -name "*.pacnew" -name "*.pacsave" -name "*.pacorig" -delete
-    # Create etc/mtab if not is a symlink.
-    if [[ ! -L "${work_dir}/root-image/etc/mtab" ]]; then
-        ln -sf "/proc/self/mounts" "${work_dir}/root-image/etc/mtab"
-    fi
     _msg_info "Done!"
 }