Revert "cli.JobExecutor: Feedback function for info output"

This reverts commit 7421df8e.

The feedback_fn argument to JobExecutor is used for PollJob, and thus
has a fixed signature: a single arg, tuple of (timestamp, log type,
log message). It's use as drop-in replacement for ToStdout doesn't
work, as that function has a different signature.

For now, I propose to revert this, until we either change JobExecutor
to use the same log messages (and add an intermediate wrapper between
JobExecutor and ToStdout) or we add another parameter to
JobExecutor.__init__.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>