message: Fix big when deleting an inserted segment in a group  op
diff: @@ -1341,12 +1341,16 @@ export class PartialSequenceLengths {
  }
  else {
  let segment = <Segment>child;
  +
  + let segBranchId = mergeTree.getBranchId(segment.clientId);
  + let removalInfo = mergeTree.getRemovalInfo(branchId, segBranchId, segment);
  +
  if (segment.seq == seq) {
  + if (removalInfo.removedSeq !== seq) {
  seqSeglen += segment.cachedLength;
  }
  + }
  else {
  - let segBranchId = mergeTree.getBranchId(segment.clientId);
  - let removalInfo = mergeTree.getRemovalInfo(branchId, segBranchId, segment);
  if (removalInfo.removedSeq === seq) {
  seqSeglen -= segment.cachedLength;
  }
  