#7387826 Launching treatment variation as new control

Proposed Changes

• This PR launches the test variant in #64239 as the new control to everybody.
• This PR also removes the Explat config to provide a clean slate for the next test.

Screenshot:

Testing Instructions

• Apply D82921-code to your sandboxed public-api.wordpress.com.
• Checkout this PR and start Calypso locally.
• Navigate to the plans step in signup and confirm that the version in the screenshot shows for all regions.
• Confirm that add-on pricing shows the accurate price and currency for a number of locations.
• Confirm that the strings are properly translated in a number of languages.
• Test the page in both large and small viewports.

Related to #

fixed Automattic/martech#824