Clean up prepared statements on remote connections at session ending
Clean up prepared statements on remote connections at session ending

This was the cause of prepared statement name conflicts when different
sessions used the same connections to remote nodes.

kmjungersen/PostgresXL,kmjungersen/PostgresXL,arcivanov/postgres-xl,Postgres-XL/Postgres-XL,pavanvd/postgres-xl,ovr/postgres-xl,zeroae/postgres-xl,oberstet/postgres-xl,arcivanov/postgres-xl,arcivanov/postgres-xl,Postgres-XL/Postgres-XL,ovr/postgres-xl,postmind-net/postgres-xl,yazun/postgres-xl,kmjungersen/PostgresXL,Postgres-XL/Postgres-XL,zeroae/postgres-xl,oberstet/postgres-xl,pavanvd/postgres-xl,techdragon/Postgres-XL,kmjungersen/PostgresXL,zeroae/postgres-xl,Postgres-XL/Postgres-XL,pavanvd/postgres-xl,oberstet/postgres-xl,techdragon/Postgres-XL,yazun/postgres-xl,postmind-net/postgres-xl,yazun/postgres-xl,snaga/postgres-xl,ovr/postgres-xl,arcivanov/postgres-xl,yazun/postgres-xl,arcivanov/postgres-xl,postmind-net/postgres-xl,arcivanov/postgres-xl,snaga/postgres-xl,postmind-net/postgres-xl,oberstet/postgres-xl,techdragon/Postgres-XL,ovr/postgres-xl,snaga/postgres-xl,techdragon/Postgres-XL,snaga/postgres-xl,postmind-net/postgres-xl,pavanvd/postgres-xl,techdragon/Postgres-XL,kmjungersen/PostgresXL,yazun/postgres-xl,Postgres-XL/Postgres-XL,snaga/postgres-xl,zeroae/postgres-xl,ovr/postgres-xl,pavanvd/postgres-xl,oberstet/postgres-xl,zeroae/postgres-xl