Fix multiple assignment of "visibility" in generate_library_loader.gni

tools/generate_library_loader/generate_library_loader.gni

 # Copyright 2014 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.
 
 # This template makes a stub for a Linux system library that dynamically loads
 # it at runtime.
 
 # name: Name to use for the value of the --name arg.
 # output_h/output_cc: Names for the generated header/cc file with no dir.
 # header: header file to process. Example: "<foo/bar.h>"
 # functions: List of strings for functions to process.
 # config: (optional) Label of the config generated by pkgconfig.
 # bundled_header: (optional)
 template("generate_library_loader") {
   output_h = "$root_gen_dir/library_loaders/" + invoker.output_h
   output_cc = "$root_gen_dir/library_loaders/" + invoker.output_cc
 
   action_visibility = [ ":$target_name" ]
   action("${target_name}_loader") {
     visibility = action_visibility
 
     script = "//tools/generate_library_loader/generate_library_loader.py"
-    if (defined(invoker.visibility)) {
-      visibility = invoker.visibility
-    }
 
     outputs = [
       output_h,
       output_cc,
     ]
 
     args = [
       "--name",
       invoker.name,
       "--output-h",
@@ skipping 25 matching lines @@
     }
     sources = [
       output_cc,
       output_h,
     ]
     public_deps = [
       ":${target_name}_loader",
     ]
   }
 }