remove panel from PoC

[pmeier]

We currently have a few instances of panel in the PoC

• https://github.com/bokeh/bokeh-fastapi/blob/23aa48d919f0221ea4a0c987e9bf9cb444749a08/test.py#L187-L192

  which is called by

  https://github.com/bokeh/bokeh-fastapi/blob/23aa48d919f0221ea4a0c987e9bf9cb444749a08/test.py#L202-L204

• https://github.com/bokeh/bokeh-fastapi/blob/23aa48d919f0221ea4a0c987e9bf9cb444749a08/test.py#L91-L98

We need to get rid of these and either

1. refactor the code to no longer need this
2. find the equivalent in bokeh
3. vendor the code

[philippjfr]

My plan would be to simple skip that branch and let Panel construct the applications before calling into bokeh-fastapi.