Revert "internal/trace: change Less to make sorting events deterministice"

This reverts commit 1764609b.

Reason for revert: It breaks the dragonfly trybot, in which there are sometimes (non-deterministically) Events with the same timestamp that have to occur in a specific order.

Change-Id: I714e640c6ab5ccb23d5577e8aa98c7716ede7ad2
Reviewed-on: https://go-review.googlesource.com/114356


Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>