Destroy all events in win32 plugin destructor

Change-Id: I59f5c9d0ed50eba1f978e13604608185a785f04b
Reviewed-on: http://review.couchbase.org/24452
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>