API PULL - Fix PHPCS and remove wrong obsolete code

[puntope]

Changes proposed in this Pull Request:

This PR fixes some PHPCS warnings created in GoogleListingAndAds.php

This was due to some old wrong code that got into the feature branch.

1. Observe this WIP commit adding some functions in GoogleListingAndAds.php -- 25db819
2. Observe this PR when we add the Jetpack functions in their own file -- Add the missing functions required for the WPCOM OAuth flow. #2145
3. Observe this commit when we remove the functions from GoogleListingAndAds.php -- 6975f77

At some point the code in point 1. Was not removed. This PR removes it.

Additionally, this PR solves PHPCS errors undetected in test files.

Detailed test instructions:

1. Follow the testing guide defined in Add the missing functions required for the WPCOM OAuth flow. #2145
2. See there are no more PHPCS errors

Additional details:

Changelog entry

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (99f5b9e) 58.5% compared to head (b4fa9c5) 58.9%.
Report is 12 commits behind head on feature/google-api-project.

Additional details and impacted files

@@                      Coverage Diff                       @@
##             feature/google-api-project   #2228     +/-   ##
==============================================================
+ Coverage                          58.5%   58.9%   +0.3%     
+ Complexity                         4248    4236     -12     
==============================================================
  Files                               458     458             
  Lines                             16919   16876     -43     
==============================================================
+ Hits                               9906    9935     +29     
+ Misses                             7013    6941     -72     

Flag	Coverage Δ
php-unit-tests	58.9% <100.0%> (+0.3%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/Google/NotificationsService.php	85.4% <100.0%> (ø)
src/Infrastructure/GoogleListingsAndAdsPlugin.php	0.0% <ø> (ø)
src/Jobs/Notifications/ProductNotificationJob.php	96.7% <100.0%> (+96.7%)	⬆️
src/Product/ProductHelper.php	95.4% <100.0%> (ø)

[jorgemd24]

Thanks for removing the old Jetpack functions and fixing the PHPCS! LGTM! 👍