Remove the |clean_up_old_dylib| gn action step

Reason for removing: It's been a while (3 years), this isn't needed anymore.

Change-Id: I2e289ebb6fb5e8f3c6786fbfa22697357617b0aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1875550
Commit-Queue: Sébastien Marchand <sebmarchand@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Auto-Submit: Sébastien Marchand <sebmarchand@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#708839}

mojo/public/cpp/system/BUILD.gn

@@ -2,23 +2,6 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# Deletes libsystem.dylib from the build dir, since it shadows
-# /usr/lib/libSystem.dylib on macOS.
-# TODO(thakis): Remove this after a while.
-action("clean_up_old_dylib") {
-  script = "//build/rm.py"
-  stamp = "$target_gen_dir/clean_up_stamp"
-  outputs = [
-    stamp,
-  ]
-  args = [
-    "--stamp",
-    rebase_path(stamp, root_build_dir),
-    "-f",
-    "libsystem.dylib",
-  ]
-}
-
 component("system") {
   output_name = "mojo_public_system_cpp"
 
@@ -79,9 +62,6 @@ component("system") {
     "//mojo/public/c/system",
     "//mojo/public/cpp/platform",
   ]
-  deps = [
-    ":clean_up_old_dylib",
-  ]
 
   defines = [ "MOJO_CPP_SYSTEM_IMPLEMENTATION" ]
 }