Use existing bash instance when running destroyScript

The destroy script already has a bash interpreter in use, but when the
`disk-deactivate` script is ran, it calls out to /usr/bin/env to query
for a bash interpreter. When running the destroyScript in unique places
(such as the stage-1 initrd), /usr/bin/env might not exist, so we can
make destroyScript more self-contained by reusing the same bash.

lib/default.nix

@@ -449,7 +449,7 @@ let
 
               # shellcheck disable=SC2043
               for dev in ${toString (lib.catAttrs "device" (lib.attrValues devices.disk))}; do
-                ${../disk-deactivate}/disk-deactivate "$dev"
+                $BASH ${../disk-deactivate}/disk-deactivate "$dev"
               done
             '';
           };