Use more precise SkSL filegroup

In http://review.skia.org/921634, Skia is removing a filegroup.
This update to PDFium will also make it so PDFium isn't building
the graphite SkSL modules (which are not used by PDFium).

Change-Id: Iabd65d7aeff8128d592066f87f24e2c4073151e6
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/126290
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Auto-Submit: Kaylee Lubick <kjlubick@google.com>
diff --git a/skia/BUILD.gn b/skia/BUILD.gn
index b160227..6f3fbb7 100644
--- a/skia/BUILD.gn
+++ b/skia/BUILD.gn
@@ -218,7 +218,7 @@
   sources += skia_sksl_pipeline_sources
   sources += skia_sksl_codegen_sources
   sources += skia_sksl_core_sources
-  sources += skia_sksl_default_module_sources
+  sources += skia_sksl_core_module_sources
   sources += skia_utils_private
   sources += skia_xps_sources
   sources += skia_codec_decode_bmp