Remove duplicate check before transfer

Before this check, the transfer is checking for the existence of the
target route in the list of selected routes twice. This change is
preliminary work for allowing the selection of the selected system route
for populating the transfer reason.

Test: Non-functional refactor.
Flag: EXEMPT refactor
Bug: b/319645714
Change-Id: I36a87790df3ffc2be2ab0f1eafee6b3096e7d4a0