Remove generated directories from include_dirs

Bug: 362796019
Change-Id: I7b42db2cb8600818c1b90e79066c282cf6596997
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/tink/+/1110327
Reviewed-by: Anivia Li <aniviali@google.com>
Commit-Queue: Steve Fung <stevefung@google.com>
Reviewed-by: Francois Rousseau <frousseau@google.com>
Fuchsia-Auto-Submit: Steve Fung <stevefung@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 2ac0f03..ef94f82 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -17,7 +17,6 @@
   ]
 
   include_dirs = [
-    "$target_gen_dir",
     "$root_gen_dir/third_party/tink/cc",
     "//third_party/tink",
   ]