port: disable zbufClear to prevent white flashing in splitscreen

src/game/zbuf.c

@@ -125,6 +125,8 @@ Gfx *zbufConfigureRdp(Gfx *gdl)
  */
 Gfx *zbufClear(Gfx *gdl)
 {
+#ifdef PLATFORM_N64
+	// no reason to do a Z clear on PC, we already do it at frame start
 	s32 left;
 	s32 right;
 
@@ -148,6 +150,7 @@ Gfx *zbufClear(Gfx *gdl)
 
 	gDPFillRectangle(gdl++, left, 0, right, playerGetFbHeight() - 1);
 	gDPPipeSync(gdl++);
+#endif
 
 	return gdl;
 }