Revert of Update FlatBuffers to include multiple improvements.

third_party/flatbuffers/flatbuffer.gni

Index: third_party/flatbuffers/flatbuffer.gni
diff --git a/third_party/flatbuffers/flatbuffer.gni b/third_party/flatbuffers/flatbuffer.gni
index f45886d37fa20c78ac23ab10819a711cc602f8ed..01527d45931d87f0efb6697022c57e2696b220cc 100644
--- a/third_party/flatbuffers/flatbuffer.gni
+++ b/third_party/flatbuffers/flatbuffer.gni
@@ -8,22 +8,11 @@
 #       Specifies the path suffix that output files are generated under. This
 #       path will be appended to root_gen_dir.
 #
-#       Targets that depend on the flatbuffer target will be able to include
-#       the resulting FlatBuffers header with an include like:
+#       Targets that depend on the proto target will be able to include the
+#       resulting flatbuffers header with an include like:
 #         #include "dir/for/my_flatbuffer/buffer_generated.h"
 #       If undefined, this defaults to matchign the input directory for each
 #       .fbs file (you should almost always use the default mode).
-#
-#   flatc_include_dirs (optional)
-#       Specifies the directories which FlatBuffers compiler uses to find
-#       included .fbs files in.
-#
-#       The directories will be tried in the order given, and if all fail (or,
-#       as by default, none are specified) it will try to load relative to the
-#       directory of the schema file being parsed.
-#
-#       TODO(pkalinnikov): Add repository root to this list, to allow including
-#       by absolute path.
 #
 #   deps (optional)
 #       Additional dependencies.
@@ -79,18 +68,8 @@
       "$out_dir/{{source_name_part}}_generated.h",
     ]
 
-    args = [ "-c" ]
-
-    if (defined(invoker.flatc_include_dirs)) {
-      foreach(include_dir, invoker.flatc_include_dirs) {
-        args += [
-          "-I",
-          rebase_path(include_dir, "$root_build_dir"),
-        ]
-      }
-    }
-
-    args += [
+    args = [
+      "-c",
       "-o",
       "$out_dir",
       "{{source}}",
@@ -122,7 +101,7 @@
     public_configs = [ "//third_party/flatbuffers:flatbuffers_config" ]
 
     public_deps = [
-      # The generated headers reference headers within FlatBuffers, so
+      # The generated headers reference headers within flatbuffers, so
       # dependencies must be able to find those headers too.
       "//third_party/flatbuffers",
     ]