* remove unnecessary explicit types
* remove dead assignments
* remove unused fields
* unindent code using early continues
* remove some unnecessary type conversions
* remove some unused func parameters

Change-Id: I202c67e92940beacbd80fc2dc179f9556dc5d9e5
Reviewed-on: https://go-review.googlesource.com/69118
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>