coreutils: fix unwanted change in prev merge

I didn't mean to change the enableParallelBuilding.

pkgs/tools/misc/coreutils/default.nix

···
 
   # Saw random failures like ‘help2man: can't get '--help' info from
   # man/sha512sum.td/sha512sum’.
-  enableParallelBuilding = true;
+  enableParallelBuilding = false;
 
   NIX_LDFLAGS = optionalString selinuxSupport "-lsepol";
   FORCE_UNSAFE_CONFIGURE = optionalString hostPlatform.isSunOS "1";