core: Expose API to elevate a thread to realtime priority

This should make it easier for clients to elevate their audio threads to
real time priority without having to dig through much through specific
system internals.

src/pulsecore/core-util.h

@@ -81,7 +81,6 @@ char *pa_strlcpy(char *b, const char *s, size_t l);
 
 char *pa_parent_dir(const char *fn);
 
-int pa_make_realtime(int rtprio);
 int pa_raise_priority(int nice_level);
 void pa_reset_priority(void);