Update firefox-ios to avoid direct use of the session token and use w…

[mhammond]

…ebchannel-specific methods instead.

This will fix the breaking change introduced in mozilla/application-services#7317

📜 Tickets

Jira ticket
Github issue

💡 Description

🎥 Demos

Before	After

Demo

📝 Checklist

• I filled in the ticket numbers and a description of my work
• I updated the PR name to follow our PR naming guidelines
• I ensured unit tests pass and wrote tests for new code
• If working on UI, I checked and implemented accessibility (Dynamic Text and VoiceOver)
• If adding telemetry, I read the data stewardship requirements and will request a data review
• If adding or modifying strings, I read the guidelines and will request a string review from l10n
• If needed, I updated documentation and added comments to complex code

[issammani]

Sweet. So happy to see this happening 😄

[mhammond]

app-services patch has been approved, so getting a review here would be great. Once all parts are reviewed I'll coordinate the landing of everything