omnisharp-roslyn: use usedotnetFromEnv instead of overriding fixup phase

  projectFile = "src/OmniSharp.Stdio.Driver/OmniSharp.Stdio.Driver.csproj";

  nugetDeps = ./deps.nix;

  useAppHost = false;

  dotnet-sdk = sdk_6_0;

  dotnet-runtime = sdk_6_0;

  dotnetInstallFlags = [ "--framework net6.0" ];

  dotnetBuildFlags = [ "--framework net6.0" "--no-self-contained" ];

    done

  '';

  dontDotnetFixup = true; # we'll fix it ourselves

  preFixup = ''

    # We create a wrapper that will run the OmniSharp dll using the `dotnet`

    # executable from PATH. Doing it this way allows it to run using newer SDK

    # versions than it was build with, which allows it to properly find those SDK

    # versions - OmniSharp only finds SDKs with the same version or newer as

    # itself. We still provide a fallback, in case no `dotnet` is provided in

    # PATH

    mkdir -p "$out/bin"

    cat << EOF > "$out/bin/OmniSharp"

    #!${stdenv.shell}

    export PATH="\''${PATH}:${sdk_6_0}/bin"

    dotnet "$out/lib/omnisharp-roslyn/OmniSharp.dll" "\$@"

    EOF

    chmod +x "$out/bin/OmniSharp"

  '';

  useDotnetFromEnv = true;

  executables = [ "OmniSharp" ];

  passthru.tests = let

    with-sdk = sdk: runCommand "with-${if sdk ? version then sdk.version else "no"}-sdk"