[sync] Automated refactor: Remove unnecessary usage of testing::_

Instead of writing METHOD_NAME(_, ..., _) when matching a method call,
one can simply use METHOD_NAME. The CL applies this change for the
following directories owned by the sync team.

components/sync
components/sync_device_info
components/sync_user_events
components/browser_sync
components/sync_preferences
components/sync_sessions
ios/components/webui/sync_internals
components/history/core/browser/sync
components/password_manager/core/browser/sync
ios/chrome/browser/sync
chrome/browser/sync
chrome/browser/ui/sync
chrome/android/java/src/org/chromium/chrome/browser/sync
chrome/test/android/javatests/src/org/chromium/chrome/test/util/browser/sync
ios/web_view/internal/sync
components/sync_bookmarks
chrome/browser/sync

Bug: None
Change-Id: Ic85900a04304ad53cd9c39d448495db32e5a0282
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2552399
Reviewed-by: Rushan Suleymanov <rushans@google.com>
Commit-Queue: Victor Vianna <victorvianna@google.com>
Cr-Commit-Position: refs/heads/master@{#830164}