relay: Avoid extra LOG_NOTICE for every new descriptor batch

Commit 56c5e282 suppressed that same log
statement in directory_info_has_arrived() for microdescriptors so do the same
for the descriptors. As the commit says, we already have the bootstrap
progress for this.

Fixes #23861

Signed-off-by: David Goulet <dgoulet@torproject.org>