Fix win/clang part 2.
Fix win/clang part 2.

After moving EmbeddedUnicodeFromCharcode the
IsValidEmbeddedCharcodeFromUnicodeCharset method is no longer used on windows.

TBR=weili@chromium.org

Review URL: https://codereview.chromium.org/1827823002 .

DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium