Move more clinit code to registration functions, part 3

Moved clinit code that fetches field/method ids
to JNI registration funcitons. This will allow to
compile-time initialize these classes.

Removed dead code in DefaultProxySelector.(java|c) that
was never called.

This is last change, remaining classes have either
dependencies that we can't work around, or required
change would make their code less maintainable.

Bug: 28153851
Change-Id: I9ef9a3c07d5cba9d4608110d94b55aada265e68f