Revert of GN: Normalize the build directory path (patchset #1 id:1 of https://codereview.chromium.org/1708513002/ )

Reason for revert:
Doesn't work on bots (link in previous comment).

Original issue's description:
> GN: Normalize the build directory path
>
> BUG=586906
> TEST=ln -s /tmp out_tmp && out/gn/gn gen out_tmp/Release
>
> Committed: https://crrev.com/89d33db3bfd53fbb3d85bb218ad4db8489a4dc34
> Cr-Commit-Position: refs/heads/master@{#375970}

TBR=hashimoto@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=586906

Review URL: https://codereview.chromium.org/1705313002

Cr-Original-Commit-Position: refs/heads/master@{#376004}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 9a3e795d6956aca4656c3c0d7d42541051b0c7c2

tools/gn/setup.cc

diff --git a/tools/gn/setup.cc b/tools/gn/setup.cc
index 831e4e4..79814e6 100644
--- a/tools/gn/setup.cc
+++ b/tools/gn/setup.cc
@@ -521,23 +521,10 @@
 }
 
 bool Setup::FillBuildDir(const std::string& build_dir, bool require_exists) {
-#if defined(OS_POSIX)
-  // Expand all ./, ../, and symbolic links in build_dir.
-  char realpath_buf[PATH_MAX];
-  if (!realpath(build_dir.c_str(), realpath_buf)) {
-    Err(Location(), "Can't normalize the build directory path.",
-        strerror(errno)) .PrintToStdout();
-    return false;
-  }
-  const std::string build_dir_realpath = realpath_buf;
-#else
-  const std::string& build_dir_realpath = build_dir;
-#endif
-
   Err err;
   SourceDir resolved =
       SourceDirForCurrentDirectory(build_settings_.root_path()).
-    ResolveRelativeDir(Value(nullptr, build_dir_realpath), &err,
+    ResolveRelativeDir(Value(nullptr, build_dir), &err,
         build_settings_.root_path_utf8());
   if (err.has_error()) {
     err.PrintToStdout();