Importer: Reconsider the "Clean Database" Option for the New Import Process

The following discussion from !1242 (merged) should be addressed:

• @suleimiahmed started a discussion: (+1 comment)

  nit: wondering if we might also benefit slightly from moving this check above the if imp.dryRun to fail early (for both dryRun and non dryRun Pre-import requests). The assumed benefit being; stopping pre-allocation of a transaction (before we are sure we need it) in the dryRun case, when a direct query against the db would suffice (for both dryRun and non-dryRun).