Revert experimental NAN patch

Hold changes from #21575 (24a095c) for more testing.

Marlin/src/gcode/probe/G30.cpp

@@ -52,7 +52,7 @@ void GcodeSuite::G30() {
 
   const ProbePtRaise raise_after = parser.boolval('E', true) ? PROBE_PT_STOW : PROBE_PT_NONE;
   const float measured_z = probe.probe_at_point(pos, raise_after, 1);
-  if (!ISNAN(measured_z))
+  if (!isnan(measured_z))
     SERIAL_ECHOLNPAIR("Bed X: ", pos.x, " Y: ", pos.y, " Z: ", measured_z);
 
   restore_feedrate_and_scaling();