#13127006 Stats: Refactoring module grid

Related to Automattic/red-team#6

Proposed Changes

• simplify Traffic grid modules by moving modules or reducing their size to half width for easier stacking
• remove UTM module feature flag after the release

Testing Instructions

• verify that the Traffic page grid works well with and without stats/devices feature flag
• test various blogs (with and without Jetpack)
• test various screen widths
• test enabling and disabling modules like Authors and Videos

Module view for versions that don’t support it:

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• https://wpcalypso.wordpress.com/devdocs/docs/testing/index.md for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the “[Status] String Freeze” label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the “[Status] Needs Privacy Updates” label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?