Revert of Refactoring gamepad polling to support dynamically added sources (patchset #5 id:80001 of https://codereview.chromium.org/1586663006/ )

Reason for revert:
Some MSan bots started failing PepperGamepadHostTest.WaitForReply after landing this, I'm going to have to assume that it's related and look at it later next week.

https://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20ChromeOS%20MSan%20Tests/builds/6775
https://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20MSan%20Tests/builds/13237

Original issue's description:
> Refactoring gamepad polling to support dynamically added sources
>
> Also reduces duplicate code between platform data fetchers by having things like
> sanitation happen in the provider, and makes the data fetchers themselves more
> modular.
>
> BUG=577414
>
> Committed: https://crrev.com/618039679323b6fc09e2146768f121661b0cdd41
> Cr-Commit-Position: refs/heads/master@{#371083}

TBR=scottmg@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=577414

Review URL: https://codereview.chromium.org/1627643002

Cr-Commit-Position: refs/heads/master@{#371138}
24 files changed