remove unused prefect-related functions

[decembboy]

@fatchat I removed unused functions kindly verify.

https://docs.google.com/spreadsheets/d/1sgh5NtW8MEcYiUcs9GaojtqsTR2Vk_zpX5bF4ef6zzs/edit#gid=0

[fatchat]

hello @decembboy

you need to fork the repo, remove the unused functions, commit and push to your forked repo, and then open a pull-request asking to merge your changes into this repo. when you do that i will be able to see your changes and either accept them or ask you to make changes before accepting

you can google "github pull request" to learn about this flow. thanks for your interest and i look forward to your PR

[fatchat]

duplicate of #542