Remove local build of plotnine

[wch]

After posit-dev/py-shiny#999 was merged into py-shiny, plotnine no longer needed a custom build for shinylive.

However, we are not able right now to use the current release version of plotnine (0.12.4), because it requires matplotlib>=3.6.0, and the version of Pyodide we are currently using includes matplotlib 3.5.2

After updating Pyodide, we will be able to switch to the newer version of plotnine.

[maartenbreddels]

I was looking into this for https://py.cafe, and this depends on pyodide/matplotlib-pyodide#52 and pyodide/pyodide#4510

[psychemedia]

Matplotlib 3.8.4 is available in pyodide 0.27.0. Related discussion here: pyodide/pyodide#5315

The current version of pyodide in shinylive seems to be 0.26.3.

[gadenbuie]

Closed by #199