Enable size_t truncation warnings in pdfium.

Bug: chromium:167187
Change-Id: If7683eef4f5234c2fffb8cae2b1329531fe1785a
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/83610
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>

BUILD.gn

diff --git a/BUILD.gn b/BUILD.gn
index 3c2f84d..7f98174 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -108,7 +108,6 @@
     ":pdfium_common_config",
     ":pdfium_public_config",
     "//build/config/compiler:noshadowing",
-    "//build/config/compiler:no_size_t_to_int_warning",
   ]
   defines = []
   if (is_win) {