[libFuzzer] remove unnecessary json.proto copy

This copy was introduced in
https://chromium-review.googlesource.com/c/chromium/src/+/746990/

But seems not necessary, can we remove this?

Bug: 938011
Change-Id: Ie32bd7737abd1353f33fb4a52068539af4d06731
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504481
Commit-Queue: Max Moroz <mmoroz@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Max Moroz <mmoroz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638110}

testing/libfuzzer/proto/BUILD.gn

@@ -4,15 +4,6 @@
 
 import("//third_party/protobuf/proto_library.gni")
 
-copy("json_proto_copy") {
-  sources = [
-    "json.proto",
-  ]
-  outputs = [
-    "$root_gen_dir" + "/testing/libfuzzer/proto/json.proto",
-  ]
-}
-
 proto_library("json_proto") {
   sources = [
     "json.proto",
@@ -21,9 +12,6 @@ proto_library("json_proto") {
   # This way json.pb.h header goes into "$root_gen_dir" directory precisely,
   # otherwise it goes into "$root_gen_dir" + "/testing/libfuzzer/proto/".
   proto_out_dir = ""
-  deps = [
-    ":json_proto_copy",
-  ]
 }
 
 source_set("json_proto_converter") {