Remove app that uses Boston housing prices dataset

ImportError:
`load_boston` has been removed from scikit-learn since version 1.2.

Author: LiamConnors

doc/python/ml-pca.md

@@ -136,23 +136,6 @@ fig.update_traces(diagonal_visible=False)
 fig.show()
 ```
 
-## PCA analysis in Dash
-
-[Dash](https://plotly.com/dash/) is the best way to build analytical apps in Python using Plotly figures. To run the app below, run `pip install dash`, click "Download" to get the code and run `python app.py`.
-
-Get started  with [the official Dash docs](https://dash.plotly.com/installation) and **learn how to effortlessly [style](https://plotly.com/dash/design-kit/) & [deploy](https://plotly.com/dash/app-manager/) apps like this with <a class="plotly-red" href="https://plotly.com/dash/">Dash Enterprise</a>.**
-
-
-```python hide_code=true
-from IPython.display import IFrame
-snippet_url = 'https://python-docs-dash-snippets.herokuapp.com/python-docs-dash-snippets/'
-IFrame(snippet_url + 'pca-visualization', width='100%', height=1200)
-```
-
-<div style="font-size: 0.9em;"><div style="width: calc(100% - 30px); box-shadow: none; border: thin solid rgb(229, 229, 229);"><div style="padding: 5px;"><div><p><strong>Sign up for Dash Club</strong> → Free cheat sheets plus updates from Chris Parmer and Adam Schroeder delivered to your inbox every two months. Includes tips and tricks, community apps, and deep dives into the Dash architecture.
-<u><a href="https://go.plotly.com/dash-club?utm_source=Dash+Club+2022&utm_medium=graphing_libraries&utm_content=inline">Join now</a></u>.</p></div></div></div></div>
-
-
 ## 2D PCA Scatter Plot
 
 In the previous examples, you saw how to visualize high-dimensional PCs. In this example, we show you how to simply visualize the first two principal components of a PCA, by reducing a dataset of 4 dimensions to 2D.