Revert "mongo-tools: fix build"

This reverts commit 3e391b839a.

This is a slower way to build the tools. Lets get this going in parallel
again. Instead of replacing the whole install process, keep the parts
which work and do just the binary copying ourselves.

pkgs/top-level/go-packages.nix

@@ -1701,11 +1701,14 @@ let
 
     # Mongodb incorrectly names all of their binaries main
     # Let's work around this with our own installer
-    buildPhase = ''
+    preInstall = ''
+      mkdir -p $bin/bin
       while read b; do
+        rm -f go/bin/main
         go install $goPackagePath/$b/main
-        mv go/bin/main go/bin/$b
+        cp go/bin/main $bin/bin/$b
       done < <(find go/src/$goPackagePath -name main | xargs dirname | xargs basename -a)
+      rm -r go/bin
     '';
   };