Revert of Use a stamp file when symlinking in GN work around mtime issues...

Revert of Use a stamp file when symlinking in GN work around mtime issues (patchset #1 id:1 of https://codereview.chromium.org/2348793002/ )

Reason for revert:
Breaks BuildPackages due to GN error (https://bugs.chromium.org/p/chromium/issues/detail?id=647706).

BUG=647706

Original issue's description:
> Use a stamp file when symlinking in GN work around mtime issues
>
> Ninja follows a symlink when stat'ing, so you can't use a symlink as an
> output and have dirty checking work properly.
> https://github.com/ninja-build/ninja/issues/1186
>
> BUG=646165
>
> Committed: https://crrev.com/fef37c4393d059c9125353928de7e49d4ea04ab4
> Cr-Commit-Position: refs/heads/master@{#419156}

TBR=dpranke@chromium.org,agrieve@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=646165

Review-Url: https://codereview.chromium.org/2348493005
Cr-Commit-Position: refs/heads/master@{#419191}

build/symlink.gni

@@ -14,17 +14,11 @@ template("symlink") {
                              "testonly",
                              "visibility",
                            ])
-
-    # Can't use the symlink itself as an output since ninja does not properly
-    # process the symlink's mtime.
-    # https://github.com/ninja-build/ninja/issues/1186
     outputs = [
-      "$target_gen_dir/$target_name.stamp",
+      invoker.output,
     ]
     script = "//build/symlink.py"
     args = [
-      "--touch",
-      rebase_path(outputs[0], root_build_dir),
       "-f",
       rebase_path(invoker.source, get_path_info(invoker.output, "dir")),
       rebase_path(invoker.output, root_build_dir),