travis, test: use Go 1.6.4, skip 'gosimple'

.travis.yml

@@ -4,8 +4,7 @@ go_import_path: github.com/coreos/etcd
 sudo: false
 
 go:
-  - 1.6
-  - tip
+  - 1.6.4
 
 env:
   global:

test

@@ -125,15 +125,6 @@ function fmt_tests {
 	fi
 
 	if which gosimple >/dev/null; then
-		echo "Checking gosimple..."
-		for path in $GOSIMPLE_UNUSED_PATHS; do
-			simplResult=`gosimple $REPO_PATH/${path} || true`
-			if [ -n "${simplResult}" ]; then
-				echo -e "gosimple checking ${path} failed:\n${simplResult}"
-				exit 255
-			fi
-		done
-	else
 		echo "Skipping gosimple..."
 	fi