Prevent remote-change event in RealtimeSyncOff mode

[chacha912]

What happened:

In the RealtimeSyncOff mode, the remote-change event is triggered unexpectedly. Previously, in #758, the remote-change event was prevented in the pushonly mode, and a similar solution is needed for the RealtimeSyncOff mode.

What you expected to happen:

Remote change events should not occur in RealtimeSyncOff mode.

How to reproduce it (as minimally and precisely as possible):

This issue occurs when switching from pushpull mode to RealtimeSyncOff mode before receiving a response to the sync request.

Anything else we need to know?:

Environment:

• Operating system:
• Browser and version:
• Yorkie version (use yorkie version):
• Yorkie JS SDK version: