[ScrollPrediction] Deleted time-based scroll prediction.

2 prediction approaches were originally added as experiments: Time-based
and frames-based. We're no longer going to pursue the time-based
approach as it doesn't make sense to choose a fixed prediction time.
Prediction should always be a function of the frame interval and as
such, we'll only be keeping the frame-based approach. This is more of a
code clean up and won't affect the current scroll prediction improvement
efforts.

Change-Id: I17ea035a4dfd296947d323afd4f65d03372b5d8e
Bug: 392817528
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6654833
Commit-Queue: Rahul Arakeri <arakeri@microsoft.com>
Reviewed-by: Jonathan Ross <jonross@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1476640}