ENG-5298: Fix use after free bug in tuple deletion.

The ElasticContext uses the tuple when being notified of deletion. If the
column it uses is not inlined, and is freed before the notification, it will
read invalid values.

Put the notification before the memory deallocation.
Merge pull request #856 from VoltDB/ENG-5298

ENG-5298: Fix use after free bug in tuple deletion.