Bazel workspace cleanup

- Remove redundant protobuf import (already imported in
   protobuf_workspace.bzl)
- Use released version of bazel buildtools instead of master to achieve
   reproducible builds

Change-Id: I92ebcfd2a0dc0352324461b9356dd348fceae2ff

WORKSPACE

@@ -143,18 +143,9 @@ load("@bazel_gazelle//:deps.bzl", "gazelle_dependencies")
 
 gazelle_dependencies()
 
-http_archive(
-    name = "com_google_protobuf",
-    strip_prefix = "protobuf-master",
-    urls = ["https://github.com/protocolbuffers/protobuf/archive/master.zip"],
-)
-
-load("@com_google_protobuf//:protobuf_deps.bzl", "protobuf_deps")
-
-protobuf_deps()
-
 http_archive(
     name = "com_github_bazelbuild_buildtools",
-    strip_prefix = "buildtools-master",
-    url = "https://github.com/bazelbuild/buildtools/archive/master.zip",
+    sha256 = "05eb52437fb250c7591dd6cbcfd1f9b5b61d85d6b20f04b041e0830dd1ab39b3",
+    strip_prefix = "buildtools-0.29.0",
+    url = "https://github.com/bazelbuild/buildtools/archive/0.29.0.zip",
 )