Revert "Enable cppgc plugin for pdfium"

This reverts commit 9140e3ff776b35ec92ae447148a2dcb739dec804.

Reason for revert: compilation warnings enable-checks-for-pdfium-directory

Original change's description:
> Enable cppgc plugin for pdfium
>
> Activate the plugin via compiler args now that the underlying issues
> have been resolved.
>
> Fixed: chromium:1421576
> Change-Id: Iafa3c8ec5b4c6f1ca8314c87bed1434269f691a5
> Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/104730
> Reviewed-by: Lei Zhang <thestig@chromium.org>
> Commit-Queue: Tom Sepez <tsepez@chromium.org>

TBR=thestig@chromium.org,tsepez@chromium.org,pdfium-scoped@luci-project-accounts.iam.gserviceaccount.com

Change-Id: I8fd5db1b18b4fc886a04d63492c07e8b32971b96
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/104830
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
diff --git a/BUILD.gn b/BUILD.gn
index 31a9026..cb1da47 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -229,10 +229,6 @@
         "-add-plugin",
         "-Xclang",
         "blink-gc-plugin",
-        "-Xclang",
-        "-plugin-arg-blink-gc-plugin",
-        "-Xclang",
-        "enable-checks-for-pdfium-directory",
       ]
     }
   }