Deprecate variables in 14.0.0

[shawnbot]

This formally deletes the following variable declarations:

• $marketingSpacers and $allSpacers (use $marketing-spacers and $marketing-all-spacers instead)
• $status-pending
• $repo-private-text, $repo-private-bg, and $repo-private-icon
• $highlight-yellow
• $exploregrid-item-border-radius
• $stats-switcher-py
• $stats-viewport-height
• $min_tab_size, $max_tab_size

I also had to make two fixes on the tool side:

1. script/dist.js now includes marketing variables dist/variables.json (so that we can compare them in script/test-deprecations.js)
2. script/test-deprecations.js doesn't throw an error if a variable that was supposed to be deprecated and doesn't exist in the most recent version of Primer. This is the case with all of our marketing variables, because we weren't previously publishing marketing variable data. 😬

[vercel]

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[simurai]

LGTM! 🚢👍