Remove unused legacy JS code after removal of legacy components and data API

Now that all legacy widget components have been removed (see #1997 and #2077) and the legacy data API as well (see #2258), we should go through the JS codebase again (after a similar issue earlier, #2418) and look for unused code that can be removed.

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Do not alter or remove anything below. The following sections will be managed by moderators only.

Acceptance criteria

• Any code including or only intended for use with legacy dashboard widgets or the legacy dataAPI should be removed (example)

Most of the definition here will be searching through the codebase.

• Note: all of this will likely not be used anymore, but if it is please note what it is in the IB with suggested replacement (if any)
• Check through all module components, and review uses of addAction and addFilter to make sure any remaining uses are still valid
• Ensure references to the old /data REST endpoint are removed (e.g in E2E request interception - search for v1/data)
• Review all TODO comments to ensure there are none left in the code that are actionable related to the removed legacy widgets and dataAPI

Implementation Brief

(See #3799 for a PR that removes request interception in E2E tests as a starting point for this issue.)

• Remove all E2E request inceptions for unused v1/data API calls
• Fix these legacy data TODOs:
  • Remove usageContext param from controlCallback in assets/js/modules/tagmanager/datastore/containers.js. This also involves changing both instances of $usage_context = $data['usageContext'] ?: self::USAGE_CONTEXT_WEB; in /Users/matt/Projects/site-kit-wp/includes/Modules/Tag_Manager.php to be $usage_context = $data['usageContext'] ?: array( self::USAGE_CONTEXT_WEB, self::USAGE_CONTEXT_AMP );
  • Remove fallback in includes/Modules/Tag_Manager.php, route GET:tag-permission, always set $container_id = $data['containerID'];
  • Remove redundant comment in tests/e2e/specs/modules/search-console/dashboard-date-range.test.js (TODO The module pages use the Widget API.)
• Remove the following, unused files:
  • assets/js/components/SignIn.js
• Remove addAction and addFilter calls:
  • addFilter( 'googlesitekit.AdSenseDashboardZeroData', 'googlesitekit.AdSenseDashboardZeroDataRefactored'
  • Refactor assets/js/components/legacy-notifications/notification-counter to call getTotalNotifications() immediately on componentDidMount()—remove the addAction() and removeAction() calls.

Test Coverage

• No tests should need removing or changing; existing tests should all pass.

Visual Regression Changes

• N/A

QA Brief

• Ensure assets/js/components/SignIn.js is gone.
• Ensure no calls to ‘v1/data’ are made.
• Ensure AC are met.

Changelog entry

• Remove unused legacy JS code after removal of legacy components and data API

[felixarntz]

@tofumatt @aaemnnosttv IB also LGTM from my end - I think it’s reasonable to make the one Tag Manager API change as well, even though that is technically a breaking change on the server-side since we’re changing the default. Should be okay this time though.

[tofumatt]

Ah, I thought that controlCallback was a safe change to make but didn’t realise the PHP part wasn’t already done. I’ve added that bit to the IB and removed some of the more aggressive changes or changes to files I thought weren’t in use but I missed their imports.

Should be ready for another look, thanks! 👍🏻