touch up exit/quit docstrings

[Sacha0]

As discussed in #22651 (review), the docstrings for exit and quit,

help?> exit
[...]
  exit([code])

  Quit (or control-D at the prompt). The default exit code is zero, indicating that the processes completed successfully.

help?> quit
[...]
  quit()

  Quit the program indicating that the processes completed successfully. This function calls exit(0) (see exit).

might benefit from a wordsmith's attention. Specifically, exit could benefit from a reference to quit, somehow integrating "control-D at the prompt" more gracefully as a synonym could be an improvement, and smoothing out the somewhat-jarring but technically correct use of plural "processes" could also be a step forward. Best!