Fix example for lcb_remove3

LCB_CMD_SET_KEY requires pointer of lcb_CMDBASE

Change-Id: I14db7430478f482ca9b2a95dd3a5875c79c758e2
Reviewed-on: http://review.couchbase.org/43069
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>