Move GREYAsserts from chrome_earl_grey into the corresponding EG tests.

This is part of EG1 to EG2 migration, which involves moving EarlGrey code from
app-side helpers into test code. For GREYAsserts, the policy is to take assert-
containing-helpers, modify them to return NSError* with localizedDescription
containing the assert failure (in the event of a failure), and then assert
on the result of the helper on the test side.

I used a Python script to automatically find ChromeEarlGrey callsites in test
code.

Bug: 922813
Change-Id: I1fdf362e9a8691c1833d19990fe551e41056e858
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1578018
Commit-Queue: ericale <ericale@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654547}