Revert "Temporary disable staticcheck" (#1568)

diff --git a/vet.sh b/vet.sh
index 9ef4837..72ef329 100755
--- a/vet.sh
+++ b/vet.sh
@@ -27,6 +27,7 @@
   go get -u \
     github.com/golang/lint/golint \
     golang.org/x/tools/cmd/goimports \
+    honnef.co/go/tools/cmd/staticcheck \
     github.com/golang/protobuf/protoc-gen-go \
     golang.org/x/tools/cmd/stringer
   if [[ "$check_proto" = "true" ]]; then
@@ -74,4 +75,4 @@
 fi
 
 # TODO(menghanl): fix errors in transport_test.
-# staticcheck -ignore google.golang.org/grpc/transport/transport_test.go:SA2002 ./...
+staticcheck -ignore google.golang.org/grpc/transport/transport_test.go:SA2002 ./...