consolidated wire+assign to just wire, with expression inlined (#1600) (#1609)

* consolidated wire <type> x; assign x = y; to wire <type> x = y;

* Remove dead code from Emitter.scala

Co-authored-by: Albert Magyar <albert.magyar@gmail.com>
(cherry picked from commit 96fbaf50

)

Co-authored-by: Murali Vijayaraghavan <vmurali@sifive.com>