ethernet: remove unit test cases that have end-to-end coverage

The removed test cases already have coverage in EthernetManagerTest and
are therefore removed. The removed tests should all be covered by
testNetworkRequest_withSingleExistingInterface.

Test: atest EthernetManagerTest
Change-Id: I5e23fc17ab10429dfb10477ff9ba546db37727ea
2 files changed