Revert "initialized git repo should use the set http_proxy"

This reverts commit 5af576ff7f.

See discussion on https://github.com/NixOS/nixpkgs/commit/5af576f

pkgs/build-support/fetchgit/nix-prefetch-git

@@ -83,7 +83,6 @@ init_remote(){
     local url=$1
     git init
     git remote add origin $url
-    [ -n "$http_proxy" ] && git config http.proxy $http_proxy
 }
 
 # Return the reference of an hash if it exists on the remote repository.