gn format BUILD.gn

Change-Id: Ifd81cf84d0c9ea4ba7dbbec212961ebd7b18424c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/253361
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

BUILD.gn

@@ -501,7 +501,7 @@ optional("gpu") {
     deps += [ ":workaround_list" ]
   }
   if (!is_fuchsia) {
-    public_defines = [ "SK_GL", ]
+    public_defines = [ "SK_GL" ]
   } else {
     public_defines = []
   }