modtimer can always be used in place of addtimer.
Do that and delete addtimer, avoiding duplicated logic.
[This is one CL in a refactoring stack making very small changes
in each step, so that any subtle bugs that we miss can be more
easily pinpointed to a small change.]
Change-Id: I70291796bdac3bef5e0850f039f6f4a1da4498ae
Reviewed-on: https://go-review.googlesource.com/c/go/+/564118 Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>