FP6: Move telephony fork to main repo on v1-a15-FP6

Description

FP6: Move telephony fork to main repo on v1-a15-FP6

Technical details

• This allows SPL merges to be directly integrated whilst having a fork.

Tests

• Run a test build to make sure sync goes well.

Issues

e/backlog#8895

10 commandments of code review

👪 ❤️ https://gitlab.e.foundation/groups/e/-/wikis/contribute/development-processes/code-review-guidelines

Summary by CodeRabbit

• Chores
  • Updated FP6 telephony component reference to a new upstream source and pinned a specific revision for improved stability and traceability.
  • Aligns remote configuration to the standard channel for more consistent updates.
  • No functional changes are expected for end-users; this is an internal alignment to support reliable builds and maintenance.