Remove useless V8 default GN args.

Support for v8_extra_library_files and
v8_experimental_extra_library_files got removed as part of
crbug.com/v8/7624 over 2 years ago.

Change-Id: Ia0904a5e7f4f35b576b004a9ad37f8908db10cd8
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/93252
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
diff --git a/.gn b/.gn
index 32c0131..748fd93 100644
--- a/.gn
+++ b/.gn
@@ -9,9 +9,6 @@
 script_executable = "python3"
 
 default_args = {
-  v8_extra_library_files = []
-  v8_experimental_extra_library_files = []
-
   # PDFs only need to run JavaScript.
   v8_enable_webassembly = false