Review and improve wallet-picker

[fayi-da]

The wallet picker was recently updated to support wallet connect. The code is somewhat sloppy and need to be cleaned up. Some ideas include:

• Clean up dead and unused css code
• Refactor inline styles and use css tokens/vars where appropriate after refactor
• connectedCallback() adds an inline message handler for wc-uri, but disconnectedCallback() does not remove it. Might cause issues
• wcUri and wcQrDataUrl are never cleared when retrying or returning to the list, so stale QR/URI datamight show up in any later attempts. Verify and clear fields appropriately if true

[mjuchli-da]

@singhyash05 keep this in mind as you implement the picker task.