Make the responsibility of initialising oximeter schema clearer

[karencfv]

Initially, oximeter was in charge of creating the oximeter database and all of its tables. With the introduction of clickhouse-admin, the responsibility now falls on reconfigurator to call clickhouse-admin and initialise the schema.

When the introduction of clickhouse-admin happened, none of the code in oximeter was touched so it still contains code to initialise the schema. It's not a problem because the operation is idempotent, but it is no longer very clear whose responsibility it is to create the database/schema.

Related: #7454