Remove custom share operator from terminal sample when it lands in the coroutines lib

[rjrjr]

Unfortunately, we had to write a custom share operator for the keystroke flow, since the keystroke worker is used by two separate workflows simultaneously, and without it they each get alternating keystrokes. There is an issue open on the coroutines project to implement a standard operator (Kotlin/kotlinx.coroutines#1261).

Originally posted by @zach-klippenstein in square/workflow@1912d58