Pretty-print when stdout is a tty; drop 'util'

This change removes `eventlogging.util` (it was never quite substantial enough
to merit being its own module) and makes `stdout_writer` pretty-print its
output when stdout is an interactive terminal.

Change-Id: I5e549dbd448db227d8c16f56c8442ded65600460
Merge "Pretty-print when stdout is a tty; drop 'util'"