Improve ExtUI, fix compiler errors, warnings (#14441)

Marlin/src/gcode/calibrate/G425.cpp

@@ -411,9 +411,13 @@ inline void probe_sides(measurements_t &m, const float uncertainty) {
     SERIAL_ECHOLNPGM("Nozzle Tip Outer Dimensions:");
     #if HAS_X_CENTER
       SERIAL_ECHOLNPAIR(" X", m.nozzle_outer_dimension[X_AXIS]);
+    #else
+      UNUSED(m);
     #endif
     #if HAS_Y_CENTER
       SERIAL_ECHOLNPAIR(" Y", m.nozzle_outer_dimension[Y_AXIS]);
+    #else
+      UNUSED(m);
     #endif
     SERIAL_EOL();
   }
@@ -518,6 +522,8 @@ inline void calibrate_toolhead(measurements_t &m, const float uncertainty, const
 
   #if HOTENDS > 1
     set_nozzle(m, extruder);
+  #else
+    UNUSED(extruder);
   #endif
 
   probe_sides(m, uncertainty);