chore(all): remove direct dependency on honnef.co/go/tools (#562)

This is now baked into the kokoro image.
diff --git a/go.mod b/go.mod
index 4e31d86..b1ccb63 100644
--- a/go.mod
+++ b/go.mod
@@ -15,5 +15,4 @@
 	google.golang.org/appengine v1.6.5
 	google.golang.org/genproto v0.0.0-20200331122359-1ee6d9798940
 	google.golang.org/grpc v1.28.0
-	honnef.co/go/tools v0.0.1-2020.1.3
 )
diff --git a/tools.go b/tools.go
index d6488bb..6fb68b8 100644
--- a/tools.go
+++ b/tools.go
@@ -9,5 +9,4 @@
 import (
 	_ "golang.org/x/lint/golint"
 	_ "golang.org/x/tools/cmd/goimports"
-	_ "honnef.co/go/tools/cmd/staticcheck"
 )