Move tools package under internal (#1141)

It is not user-facing, so there is no reason to leave it in an
importable location. Fixes #1126.

internal/tools/tools.go

@@ -0,0 +1,24 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build tools
+
+package tools
+
+import (
+	_ "github.com/client9/misspell/cmd/misspell"
+	_ "github.com/golangci/golangci-lint/cmd/golangci-lint"
+	_ "github.com/itchyny/gojq"
+	_ "golang.org/x/tools/cmd/stringer"
+)