Remove Voice pitch clamp (and fix use of incorrect constant)

[jjohnsnaill]

This is a limitation inherited from XNA that FNA has long since been able to handle, and MoonWorks' pitch tweening supports values beyond -1 and 1 already.
Additionally, SourceVoice has inherited FNA-XNA/FNA#519 and the fix has yet to be made in MoonWorks as well.