[Background Fetch] Remove deprecated proto field.

The field was deprecated in M71, and is no longer needed

Change-Id: I258b64134cbd95fd99d1a57d43c94d204bd46251
Reviewed-on: https://chromium-review.googlesource.com/c/1426684
Reviewed-by: Mugdha Lakhani <nator@google.com>
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624908}
2 files changed