Remove deprecation trigger at MigrateTools::addToSyncSourceIds in 7.x

Problem/Motivation

In 🐛 sync might be too strict during id comparison; rolls back everything Needs review a deprecation warning was added for 6.x

Steps to reproduce

Check MigrateTools::addToSyncSourceIds

Proposed resolution

Remove deprecation warning in 7.x

Remaining tasks

Remove deprecation

User interface changes

N/A

API changes

N/A

Data model changes

N/A