Remove wfi in examples

[ssnover]

This PR removes wfi from examples. I ran into an issue flashing code onto my board after flashing one of the examples and found this thread which finally gave me the method I needed to erase the code flash.

Since these are examples and power consumption is not a big deal, I think it's not necessary to use wfi and instead just let the microcontroller processor spin. Seems better than pushing someone through some general headache around the board no longer being connectable via SWD. I did leave it as-is in examples/timer-interrupt-rtic.rs as I'm less certain of it's necessity in an RTIC context.