Remove possible unused codebook entries about optivorbis

[AlexTMjugador]

Hi, thanks for trying out OptiVorbis!

Regarding your question:

• The first highlighted vorbis string is required by the Vorbis specification to be present: it is the Vorbis identification packet header signature.
• The second highlighted OggS string is the Ogg page capture pattern, which is required by the Ogg container specification to signal the beginning of a page. The Vorbis specification requires that this second page is present: the identification header must be alone on its own page.
• The second highlighted vorbis string is required, and it is used as the Vorbis comment header signature, which is mandatory.
• The third highlighted vorbis string, which is followed by the codebook count and the sync pattern BCV for the first codebook, is also required by the Vorbis specification.
• The highlighted mostly-zero bytes may be optimized further. It's difficult to say for sure without proper analysis, but they look like unused codebook entries, and it looks feasible to remove them, although doing it properly is a bit complicated and not implemented yet.