[Feature] Disable REPL button if not supported

[laurensvalk]

Is your feature request related to a problem? Please describe.
Now that the Move Hub informs Pybricks Code about the (lack of) REPL support, we could disable that button.

We could then also omit the REPL not supported! message and associated checks in micropython.c and save a bit on build size like pybricks/pybricks-micropython@4775a08

This also has the benefit of not showing a somewhat confusing REPL not supported! when raising a KeyboardInterrupt.

[laurensvalk]

I'll go ahead and prepare the firmware side of it. EDIT: Since this is quite non-intrusive, I've gone ahead and merged it.