consolidated wire+assign to just wire, with expression inlined (bp #1600 to 1.2.x) (#1611)

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

* 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>

* Backport to 1.2.x

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