bootstrap tools: have curl without http2 support

I assume there's not much use for it during bootstrapping.
This fixes them as well, as curl was compiled against libnghttp2 but the
lib wasn't copied to the bootstrap tools.

pkgs/stdenv/linux/make-bootstrap-tools.nix

@@ -11,6 +11,7 @@ rec {
   });
 
   curlMinimal = curl.override {
+    http2Support = false;
     zlibSupport = false;
     sslSupport = false;
     scpSupport = false;