main : add cli option to disable system prints

[ggerganov]

close #1735, #1448

Use the -np flag to suppress all irrelevant prints:

$ ▶ ./main -f samples/jfk.wav -np

[00:00:00.000 --> 00:00:11.000]   And so my fellow Americans, ask not what your country can do for you, ask what you can do for your country.

$ ▶ ./main -f samples/jfk.wav -np -nt

 And so my fellow Americans, ask not what your country can do for you, ask what you can do for your country.