StreamManager Client might not be cleaning up after itself when no longer used

[nicknezis]

Describe the bug
Reviewing the stmgr C++ code, I am not able to find where the StmgrClient pointer is deleted. I believe this should be happening in the HandleClose callback as is done in chkptmgr-client.cpp.

We should test with HEAPCHECK_ENABLED=1 to verify that there is not a leak.

This might be related to #3492