Update dcc.Markdown for react 18 compatibility

[T4rk1n]

@T4rk1n
I just noticed that dcc.Mardown generates a warning in the console - which is weird because it's not a function component.
Warning: v: Support for defaultProps will be removed from function components in a future major release. Use JavaScript default parameters instead. Error Component Stack

from dash import Dash, dcc

app=Dash()
app.layout = dcc.Markdown("I have a console warning")

if __name__ == "__main__":
    app.run(debug=True)

Originally posted by @AnnMarieW in #3148

[gvwilson]

Are we OK accepting that MathJax will always be loaded with the Markdown component? (approx. 2 Mbyte)