[Revamp Landing Screen] Remove old landing screen & all code related to it

[ovitrif]

Remove the code for the previous landing screen once the new screen is enabled from both:

• WordPress App
• Jetpack App

Since the carousel was removed from the landing screen of the WordPress Android app, we should also cleanup the analytics event tracking code that was responsible for tracking carousel events.

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This issue cannot be solved for as long the Revamped Landing Screen can be toggled on/off with a feature flag.