removeReferencesTo: correct region reference in fixupHook

This was causing some regions to escape the fixupHook. As a concrete
example, pkgconf's signature on aarch64-darwin was not valid because
the library was not fixed up.

pkgs/build-support/remove-references-to/remove-references-to.sh

@@ -32,6 +32,6 @@ done
 
 for region in "${regions[@]}"; do
     for hook in "${fixupHooks[@]}"; do
-        eval "$hook" "$i"
+        eval "$hook" "$region"
     done
 done