Don't generate /etc/classpath in make.

Soong generates classpaths.proto config and puts it into
/system/etc/classpaths/ for derive_classpath to read at runtime. There
is no need to plumb these values via make anymore.

Bug: 180105615
Test: m && launch_cvd; presubmit / DeviceBootTest
Change-Id: I514c5036871233ae865b972effea8321dbe4aea9