Bandwidth Savings Predictor changes for Chromium 83.

[mkarolin]

This Chromium change (landing in Cr83) has removed

  // The first time the page is considered 'interactive'. This is determined
  // using heuristics based on main thread and network activity. Time delta is
  // relative to navigation_start.
  mojo_base.mojom.TimeDelta? interactive;

value from struct InteractiveTiming.

Underlying Chromium issue: https://bugs.chromium.org/p/chromium/issues/detail?id=1055806

A commit in brave/brave-core#5102 (WIP for upgrade to Cr83) named InteractiveTiming.interactive was removed from page load metrics. removes direct use of the field from the bandwidth savings predictor, but doesn't touch the model components/brave_perf_predictor/python/resources, which uses the field.

This is a followup issue to determine what needs to happen in the model (or if the interactive field needs to be restored in the code).

cc: @bsclifton

[bsclifton]

Setting missing milestone to 1.10