libSceOpusCeltDec technical debt

sceOpusCeltDecCreateEx, sceOpusCeltDecDecode, sceOpusCeltDecDestroy, sceOpusCeltDecGetSize, sceOpusCeltDecInitialize, sceOpusCeltDecTerminate (libSceOpusCeltDec) - imported by PPSA99001, which fails to load without the module; added without an implementation. Their signatures match libSceOpusDec's in ProsperoRadio. PPSA99001 opens this decoder only as a fallback when libSceOpusDec reports a retryable error for a CELT packet, which libSceOpusDec here never returns, so the fallback is not reached