Revert "cros: Convert switch to feature for new overview ui."

This reverts commit e50412fb9216127a3818a3682e94633d7af7da66.

Reason for revert: crbug.com/821999 enabled test now failing on chromeos

Original change's description:
> cros: Convert switch to feature for new overview ui.
> 
> Convert to feature which is enabled by default.
> 
> Test: manual
> Bug: 821608
> Change-Id: If513c4d2a6bdfd4197525d7922d99cfc01f4c616
> Reviewed-on: https://chromium-review.googlesource.com/961721
> Reviewed-by: Scott Violet <[email protected]>
> Commit-Queue: Sammie Quon <[email protected]>
> Cr-Commit-Position: refs/heads/master@{#543139}

[email protected],[email protected]

Change-Id: I92ce3f93cb88cef92e242fbbd6338cbdac528cdd
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 821608
Reviewed-on: https://chromium-review.googlesource.com/962837
Reviewed-by: Caleb Rouleau <[email protected]>
Commit-Queue: Caleb Rouleau <[email protected]>
Cr-Commit-Position: refs/heads/master@{#543205}
12 files changed