progress: drop delay-threshold code

progress: drop delay-threshold code

Since 180a9f2268 (provide a facility for "delayed" progress
reporting, 2007-04-20), the progress code has allowed
callers to skip showing progress if they have reached a
percentage-threshold of the total work before the delay
period passes.

But since 8aade107dd (progress: simplify "delayed" progress
API, 2017-08-19), that parameter is not available to outside
callers (we always passed zero after that commit, though
that was corrected in the previous commit to "100%").

Let's drop the threshold code, which never triggers in
any meaningful way.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>