singularity-tools: drop override argument storeDir

  Processes also now run as a dynamically allocated user by default instead of

  root.

- `singularity-tools` have the `storeDir` argument removed from its override interface and use `builtins.storeDir` instead.

- The `budgie` and `budgiePlugins` scope have been removed and their packages

  moved into the top level scope (i.e., `budgie.budgie-desktop` is now

  `budgie-desktop`)

  bashInteractive,

  runtimeShell,

  singularity,

  storeDir ? builtins.storeDir,

}:

let

            # Run root script

            ${lib.optionalString (runAsRoot != null) ''

              mkdir -p ./${storeDir}

              mount --rbind ${storeDir} ./${storeDir}

              mkdir -p ./${builtins.storeDir}

              mount --rbind "${builtins.storeDir}" ./${builtins.storeDir}

              unshare -imnpuf --mount-proc chroot ./ ${runAsRootFile}

              umount -R ./${storeDir}

              umount -R ./${builtins.storeDir}

            ''}

            # Build /bin and copy across closure