Deprecate transactionManagerLookup attribute

Our current JSON schema includes under storage an attribute named transactionManagerLookup. In the past, this could be used to specify the fully qualified name of the Infinispan transaction manager lookup.

However, since the introduction of Environment class, this has become obsolete and is ignored atm. We should deprecate it in the schema (via a comment), remove unused code and remove it from the test configurations where it's being used.

If there are tests that need/should run with a specific lookup (e.g. Dummy may be faster) then this should be done via a TestingEnvironment.