Remove corepkgs/config.nix

This isn't used anywhere except in the configure script of the Perl
bindings. I've changed the latter to use the C++ API's Settings object
at runtime.

perl/lib/Nix/Store.xs

@@ -351,3 +351,13 @@ void addTempRoot(char * storePath)
         } catch (Error & e) {
             croak("%s", e.what());
         }
+
+
+SV * getBinDir()
+    PPCODE:
+        XPUSHs(sv_2mortal(newSVpv(settings.nixBinDir.c_str(), 0)));
+
+
+SV * getStoreDir()
+    PPCODE:
+        XPUSHs(sv_2mortal(newSVpv(settings.nixStore.c_str(), 0)));