Remove aos/protobuf

Doesn't look like anyone is using it

Change-Id: I35316d58596ad8b72a060de281cdb044c61e6f75
diff --git a/aos/protobuf/BUILD b/aos/protobuf/BUILD
deleted file mode 100644
index 6e61139..0000000
--- a/aos/protobuf/BUILD
+++ /dev/null
@@ -1,24 +0,0 @@
-package(default_visibility = ["//visibility:public"])
-
-cc_library(
-    name = "stack_arena",
-    srcs = ["stack_arena.cc"],
-    hdrs = ["stack_arena.h"],
-    target_compatible_with = ["@platforms//os:linux"],
-    deps = [
-        "//aos/logging",
-        "@com_google_protobuf//:protobuf",
-    ],
-)
-
-cc_test(
-    name = "stack_arena_test",
-    srcs = ["stack_arena_test.cc"],
-    target_compatible_with = ["@platforms//os:linux"],
-    deps = [
-        ":stack_arena",
-        "//aos/logging",
-        "//aos/testing:googletest",
-        "//aos/testing:test_logging",
-    ],
-)
diff --git a/aos/protobuf/stack_arena.cc b/aos/protobuf/stack_arena.cc
deleted file mode 100644
index c085fcb..0000000
--- a/aos/protobuf/stack_arena.cc
+++ /dev/null
@@ -1,15 +0,0 @@
-#include "aos/logging/logging.h"
-
-namespace aos {
-namespace protobuf {
-
-void FatalArenaBlockAlloc(size_t) {
-  AOS_LOG(FATAL, "trying to allocate in arena code");
-}
-
-void FatalArenaBlockDealloc(void*, size_t) {
-  AOS_LOG(FATAL, "trying to deallocate in arena code");
-}
-
-}  // namespace protobuf
-}  // namespace aos
diff --git a/aos/protobuf/stack_arena.h b/aos/protobuf/stack_arena.h
deleted file mode 100644
index 28c933c..0000000
--- a/aos/protobuf/stack_arena.h
+++ /dev/null
@@ -1,52 +0,0 @@
-#ifndef AOS_PROTOBUF_STACK_ARENA_H_
-#define AOS_PROTOBUF_STACK_ARENA_H_
-#include "google/protobuf/arena.h"
-
-namespace aos {
-namespace protobuf {
-
-void* FatalArenaBlockAlloc(size_t);
-
-void FatalArenaBlockDealloc(void*, size_t);
-
-// This class manages a protobuf arena which uses an internal buffer
-// (allocated as part of the object) of size buffer_size.
-//
-// Protos allocated from this arena must not use more than buffer_size
-// worth of data.
-//
-// Also worth noting is that sizeof(google::protobuf::Arena::Block)
-// is used up out of the buffer for internal protobuf related usage, so
-// overallocate accordingly.
-template <size_t buffer_size>
-class StackProtoArena {
- public:
-  StackProtoArena() :
-      arena_(GetArenaOptions(&data_[0])) {}
-
-  google::protobuf::Arena* arena() { return &arena_; }
-
-  // For convienence:
-  template <typename T>
-  T* CreateMessage() {
-    return google::protobuf::Arena::CreateMessage<T>(&arena_);
-  }
- private:
-  static google::protobuf::ArenaOptions GetArenaOptions(char* data) {
-    // Expecting RVO to kick in.
-    google::protobuf::ArenaOptions options;
-    options.initial_block = data;
-    options.initial_block_size = buffer_size;
-    options.block_alloc = &FatalArenaBlockAlloc;
-    options.block_dealloc = FatalArenaBlockDealloc;
-    return options;
-  }
-
-  char data_[buffer_size];
-  google::protobuf::Arena arena_;
-};
-
-}  // namespace protobuf
-}  // namespace aos
-
-#endif  // AOS_PROTOBUF_STACK_ARENA_H_
diff --git a/aos/protobuf/stack_arena_test.cc b/aos/protobuf/stack_arena_test.cc
deleted file mode 100644
index a07ceea..0000000
--- a/aos/protobuf/stack_arena_test.cc
+++ /dev/null
@@ -1,30 +0,0 @@
-#include "gtest/gtest.h"
-
-#include "aos/logging/logging.h"
-#include "aos/protobuf/stack_arena.h"
-#include "aos/testing/test_logging.h"
-
-namespace aos {
-namespace protobuf {
-namespace {
-
-struct TestStruct {
-  int a;
-  int b;
-  int c;
-};
-
-class StackProtoArenaTest : public ::testing::Test {};
-
-TEST_F(StackProtoArenaTest, Basic) {
-  ::aos::testing::EnableTestLogging();
-  StackProtoArena<164> stack_arena;
-
-  TestStruct* msg =
-      google::protobuf::Arena::Create<TestStruct>(stack_arena.arena());
-  AOS_CHECK_NOTNULL(msg);
-}
-
-}  // namespace
-}  // namespace protobuf
-}  // namespace aos