ethernet: remove EthernetManager shims

These shims were used for when T APIs were not available on
sc-mainline-prod. Since we have moved on to using tm-mainline-prod, this
is not a problem anymore.

Bug: 171872016
Test: builds && TH
Change-Id: I895ea523c6acb23ff64b7ce16da2dc3d246b2f37
(cherry picked from commit cf0f2186b2a76eef0dd87da5e4186db4446b65a6)
Merged-In: I895ea523c6acb23ff64b7ce16da2dc3d246b2f37