Drop the pycall dependency

[findmyway]

• [ ] Update the backend to C++
• [ ] Update Docs link (because now it is moved into the Ju-jl org)
• [ ] Update Registry
  • How?
  • Or just update in Ju-jl/Registry?

[findmyway]

Ref: https://github.com/PaddlePaddle/VisualDL/pull/529