Remove unnecessary virtual specifiers

Clang has added a new warning for virtual specifiers on methods of
`final` classes. This cleans them up in preparation for enabling that
warning.

Bug: chromium:403236787
Change-Id: If24967947b9ba1ded80fe6c3008944efbc013bd8
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/129910
Auto-Submit: Devon Loehr <dloehr@google.com>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Thomas Sepez <tsepez@google.com>
Reviewed-by: Thomas Sepez <tsepez@google.com>
Commit-Queue: Devon Loehr <dloehr@google.com>
diff --git a/core/fxcodec/progressive_decoder.h b/core/fxcodec/progressive_decoder.h
index 2de8c96..3f4ca89 100644
--- a/core/fxcodec/progressive_decoder.h
+++ b/core/fxcodec/progressive_decoder.h
@@ -67,7 +67,7 @@
   };
 
   ProgressiveDecoder();
-  virtual ~ProgressiveDecoder();
+  ~ProgressiveDecoder();
 
   FXCODEC_STATUS LoadImageInfo(RetainPtr<IFX_SeekableReadStream> pFile,
                                FXCODEC_IMAGE_TYPE imageType,