tracef-tracelog-limitations.txt: take variadic variant into account

This patch changes `tracef-tracelog-limitations.txt` so as to always
mention the variadic variant where the non-variadic variant is mentioned
for consistency.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I13250fdae647ea58c042238c88b674c56d4f3fc0