scriptlive: reduce two usage synopses to one simple one

scriptlive: reduce two usage synopses to one simple one

No synopsis can show all possible permutattions of arguments and
options, so do not even try and just give the most basic form,
without unneeded -t, -I, or -B.

Also, use angle brackets to show that <timingfile> and <typescript>
are placeholders.

Signed-off-by: Benno Schulenberg <bensberg@telfort.nl>
(cherry picked from commit 921b4fe498edde7d1d5c280d6d50050d18d97b44)