The `attemptToMigrateByCreatingOnService` method has a single caller,
and that caller also calls `tryToPrepareMembersForMigration` first. The
former is called when `migrationMode`’s `canMigrateToService` is true,
and the latter does a CDS lookup & profile key fetches if
`migrationMode`’s `isOnlyUpdatingIfAlreadyMigrated` is false; these two
conditions are true in the same situations. As a result, these CDS
lookups and profile key fetches aren’t necessary.
(This also removes an extra `firstly` block. I’d recommend ignoring
whitespace while reviewing the change.)
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