Incorrect pass of MemberId in LeaveGroupRequest

[nerhneiro]

In LeaveGroup method of versions <= 2 MemberId for the consumer that is in the process of leaving a group is passed in MemberId field. While in versions >= 3 MemberId is stored in the list of members for each member specified. However, memberId is expected to be passed in MemberId field, otherwise it is empty and an error occurs.