Partially revert "Update CHANGELOG for Firestore v0.14.0 (#2025)" (#2031)
Partially revert "Update CHANGELOG for Firestore v0.14.0 (#2025)" (#2031)

This removes the changelog entry that describes our migration to
gRPC-C++.
firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk,firebase/firebase-ios-sdk