Reduced transaction dependencies of logserver automatic index deletion

The logserver process (session 4) is responsible for dropping no longer needed indices. To accomplish this, the logserver checks once a day at midnight all indices for their lifetimes. This check read locks every table in the database.

Problem
There is a small chance that these logserver tasks cause user ETL sessions to be forcefully rolled back (transaction conflicts).

Improvement
The index deletion process has been improved to isolate read locking of all tables in a special transaction. Hence dependencies to user transactions are reduced.