Update //third_party/protobuf to version 3.

third_party/protobuf/cleanup_release.sh

+#!/bin/bash
+
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+
+cd $DIR
+
+rm -f appveyor.*
+rm -f autogen.sh
+rm -rf benchmarks/
+rm -f BUILD
+rm -rf cmake/
+rm -f configure.ac
+rm -rf conformance/
+rm -rf csharp/
+rm -rf editors/
+rm -rf examples/
+rm -f generate_descriptor_proto.sh
+rm -f .gitignore
+rm -f gmock.BUILD
+rm -f INSTALL.txt
+rm -rf java/
+rm -rf javanano/
+rm -rf js/
+rm -rf m4/
+rm -rf Makefile.am
+rm -rf more_tests/
+rm -rf objectivec/
+rm -f post_process_dist.sh
+rm -f protobuf.bzl
+rm -f protobuf-lite.pc.in
+rm -f protobuf.pc.in
+rm -f Protobuf.podspec
+rm -rf protoc-artifacts/
+rm -rf ruby/
+rm -f six.BUILD
+rm -f travis.sh
+rm -f .travis.yml
+rm -f update_file_lists.sh
+rm -rf util/
+rm -f WORKSPACE
+
+# src/
+rm -rf src/solaris/
+rm -f src/Makefile.am
+
+# src/google/protobuf/compiler/
+rm -rf src/google/protobuf/compiler/csharp
+rm -rf src/google/protobuf/compiler/java
+rm -rf src/google/protobuf/compiler/javanano
+rm -rf src/google/protobuf/compiler/js
+rm -rf src/google/protobuf/compiler/objectivec
+rm -rf src/google/protobuf/compiler/ruby