Remove dead declaration

This code was removed a while ago, but the declaration for it was left
around for some reason.

sim.h

@@ -14,8 +14,6 @@ static inline Piano_bits piano_bits_of(Glyph g) {
   return UINT64_C(0);
 }
 
-void init_random_seed(Usz value);
-
 void orca_run(Glyph* restrict gbuffer, Mark* restrict mbuffer, Usz height,
               Usz width, Usz tick_number, Oevent_list* oevent_list,
               Piano_bits piano_bits, Usz random_seed);