fix: remove error listener to prevent memory leak (#1168)
fix: remove error listener to prevent memory leak (#1168)

Getting a session would set a new event listener on the session pool that
would not always be removed. The event listener is now removed after each
call.

Co-authored-by: skuruppu <382bd9679e6cb7e2135c45a8cd1be9e02cd75f23@google.com>
googleapis/nodejs-spanner,googleapis/nodejs-spanner,googleapis/nodejs-spanner,googleapis/nodejs-spanner