fix lint

Author: martinbonnin

firebase-firestore/ktx/src/main/kotlin/com/google/firebase/firestore/ktx/Firestore.kt

@@ -30,7 +30,6 @@ import com.google.firebase.firestore.QueryDocumentSnapshot
 import com.google.firebase.firestore.QuerySnapshot
 import com.google.firebase.ktx.Firebase
 import com.google.firebase.platforminfo.LibraryVersionComponent
-import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.cancel
 import kotlinx.coroutines.channels.Channel
 import kotlinx.coroutines.channels.awaitClose
@@ -240,4 +239,4 @@ fun Query.toFlow(
     } else {
         flow
     }
-}
+}