remove duplicate parellel function

[HexSleeves]

I used threaded feature and it threw some errors so this is removing the duplicated function. There is also a missing function build_parallel_weighted

[HexSleeves]

Ah did some digging and it turns out you handle the threaded feature on the build_helper threaded function. I removed the unused function

[thebracket]

Tested this locally and merged - thank you!