Remove `update_share` method from the case endpoint

The below method

https://github.com/TheHive-Project/TheHive4py/blob/8ee22485e963e9fba168a2f6c74f4a1a9fc882b7/thehive4py/endpoints/case.py#L172

is apparently not part of TheHive API anymore.

Let's remove it as it anyways never really worked.


 