Refactored smells out of query_runner/database_on_demand.rb

Smells reported by reek:

Before:

 1: NoBrainer::QueryRunner::DatabaseOnDemand has no descriptive
    comment (IrresponsibleModule)
 5: NoBrainer::QueryRunner::DatabaseOnDemand#call has the variable
    name 'e' (UncommunicativeVariableName)
 2: NoBrainer::QueryRunner::DatabaseOnDemand#call refers to env more
    than self (FeatureEnvy)

After:

 1: NoBrainer::QueryRunner::DatabaseOnDemand has no descriptive
    comment (IrresponsibleModule)

Notes:

All specs pass after this change, but it appears that this specific
functionality is not tested. So, I've only made trivial changes.