garlicd: drop bscpkgs argument requirement

The bscpkgs/default.nix is not longer read, as the garlic tool only
needs it for the fetching (-F), when it runs nix-build.

garlic/garlicd/garlicd

@@ -6,15 +6,13 @@ msg() {
   >&2 echo "garlicd: $@"
 } 
 
-if [ -z "$1" ]; then
-  >&2 echo "usage: garlicd <bscpkgs directory>"
+if [ ! -z "$1" ]; then
+  >&2 echo "usage: garlicd"
   exit 1
 fi
 
 export PATH="@extraPath@:$PATH"
 
-bscpkgsdir=$(readlink -f "$1")
-
 garlic_sandbox=$(nix show-config |\
   grep extra-sandbox-paths |\
   grep -o '/garlic=[^ ]*' || true)
@@ -47,8 +45,6 @@ for fifo in "$run" "$completed" "$wipe"; do
   fi
 done
 
-cd "$bscpkgsdir"
-
 while true; do
   msg "Waiting for experiments ..."
   read -r tre < "$run"