C API - Remove function definitions for functions that do not exist
C API - Remove function definitions for functions that do not exist

In libspeechd.h, there are the following function definitions:
int spd_set_synthesis_voice(SPDConnection*, const char *voice_name);
int spd_set_synthesis_voice_type_all(SPDConnection*, const char *voice_name);
int spd_set_synthesis_voice_type_uid(SPDConnection*, const char *voice_name, unsigned int uid);

However, these functions do not exist in libspeechd.c, so remove the
definitions.

razr/speechd,razr/speechd,razr/speechd,razr/speechd