Don't mount the nix store in owl nodes

Initially we planned to run jobs in those nodes by sharing the same nix
store from hut. However, these nodes are now used to build packages
which are not available in hut. Users also ssh to the nodes, which
doesn't mount the hut store, so it doesn't make much sense to keep
mounting it.

Reviewed-by: Aleix Boné <abonerib@bsc.es>

m/owl1/configuration.nix

@@ -7,7 +7,6 @@
     ../module/emulation.nix
     ../module/slurm-client.nix
     ../module/slurm-firewall.nix
-    ../module/slurm-hut-nix-store.nix
     ../module/debuginfod.nix
   ];
 

m/owl2/configuration.nix

@@ -7,7 +7,6 @@
     ../module/emulation.nix
     ../module/slurm-client.nix
     ../module/slurm-firewall.nix
-    ../module/slurm-hut-nix-store.nix
     ../module/debuginfod.nix
   ];