Deletes header files and BUILD targets for SpdyUnsafeArena, which is no longer used.

gfe-relnote: n/a (deletes unused code/BUILD targets)
PiperOrigin-RevId: 284816046
Change-Id: I69f074a61077fc8396448c2524ea5387c57a46ab

spdy/platform/api/spdy_unsafe_arena.h

diff --git a/spdy/platform/api/spdy_unsafe_arena.h b/spdy/platform/api/spdy_unsafe_arena.h
deleted file mode 100644
index 77185e1..0000000
--- a/spdy/platform/api/spdy_unsafe_arena.h
+++ /dev/null
@@ -1,16 +0,0 @@
-// Copyright (c) 2019 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef QUICHE_SPDY_PLATFORM_API_SPDY_UNSAFE_ARENA_H_
-#define QUICHE_SPDY_PLATFORM_API_SPDY_UNSAFE_ARENA_H_
-
-#include "net/spdy/platform/impl/spdy_unsafe_arena_impl.h"
-
-namespace spdy {
-
-using SpdyUnsafeArena = SpdyUnsafeArenaImpl;
-
-}  // namespace spdy
-
-#endif  // QUICHE_SPDY_PLATFORM_API_SPDY_UNSAFE_ARENA_H_