Cleanup protobuf response

[chacha912]

Description:

Remove unnecessary client information from the protobuf response.

We are currently returning client_id or client_key as follows:
https://github.com/yorkie-team/yorkie/blob/main/api/yorkie/v1/yorkie.proto#L41-L116

message ActivateClientResponse {
  string client_key = 1;
  bytes client_id = 2;
}

message DeactivateClientResponse {
  bytes client_id = 1;
}

message AttachDocumentResponse {
  bytes client_id = 1;
  string document_id = 2;
  ChangePack change_pack = 3;
}

message DetachDocumentResponse {
  string client_key = 1;
  ChangePack change_pack = 2;
}

message RemoveDocumentResponse {
  string client_key = 1;
  ChangePack change_pack = 2;
}

message PushPullChangesResponse {
  bytes client_id = 1;
  ChangePack change_pack = 2;
}

We only need to return the client_id when activating, and the rest seems unnecessary.
It would be better to clean up.

Why:
to make protobuf concise

[hackerwins]

Tasks

• Go SDK: Cleanup proto #614
• JS SDK: Cleanup proto yorkie-js-sdk#617
• Android SDK: Concurrent case handling for Yorkie.tree yorkie-android-sdk#131
• iOS SDK: Cleanup proto yorkie-ios-sdk#101