Remove system_server_current related work arounds

Previously, a library that set sdk_version: "system_server_current"
could only access system-server or public APIs from other libraries.
After change r.android.com/2238635 they will be able to access the
following (in order):
* system-server
* module-lib
* system
* public

Ignore-AOSP-First: AOSP change conflicts with this branch.
Bug: 204176972
Test: m com.android.tethering
      # Without change r.android.com/2238635 the affected libraries
      # fail to compile due to missing symbols that are not in the
      # public API. With that change it compiles correctly.
Change-Id: Id6aad00aed0af6b724afec663a7be287058e625e