GH-2051: Update (remove) In-App Plus/Premium pricing

[benstrumeyer]

• Have you followed the guidelines in CONTRIBUTING.md?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you added an explanation of what your changes do?
• Does your submission pass tests?
• Did you lint your code prior to submission?

Remove pricing in:

• In-App Plus Promo Panel
• Intro Hub Plus Tab
• The $2 tag next to Get Ghostery Plus tab in the Hub
• The upsell popup in the Historical Stats view
• Subscription Tab (no active subscriptions) is handled in account-web https://github.com/ghostery/account-web/pull/91
• Spring Plus Promo is already updated

[wlycdgr]

I'm still seeing the $2 price in a couple spots:

• The Get Ghostery Plus tab in the Hub
• The upsell popup in the HIstorical Stats view

[wlycdgr]

Can you add the period back in?

[benstrumeyer]

Added back in--I still can't believe you caught that

[wlycdgr]

LGTM