Removes the objects in the range start inclusive to end exclusive.
The start and end indices must be in the range
0 ≤ index ≤ length, and start ≤ end.
Throws an UnsupportedError if this is a fixed-length list. In that case
the list is not modified.
void removeRange(int start, int end) {
_rangeCheck(start, end);
int rangeLength = end - start;
int len = _list.length;
_notifyChangeLength(len, len - rangeLength);
if (hasListObservers && rangeLength > 0) {
_recordChange(new ListChangeRecord(this, start,
removed: _list.getRange(start, end).toList()));
}
_list.removeRange(start, end);
}