Fix ExtUI compile (#17834)

Marlin/src/lcd/extui_example.cpp

@@ -89,6 +89,7 @@ namespace ExtUI {
     // whether successful or not.
   }
 
+  #if HAS_MESH
     void onMeshUpdate(const int8_t xpos, const int8_t ypos, const float zval) {
       // Called when any mesh points are updated
     }
@@ -96,6 +97,7 @@ namespace ExtUI {
     void onMeshUpdate(const int8_t xpos, const int8_t ypos, const ExtUI::probe_state_t state) {
       // Called to indicate a special condition
     }
+  #endif
 
   #if ENABLED(POWER_LOSS_RECOVERY)
     void onPowerLossResume() {

Marlin/src/lcd/extui_malyan_lcd.cpp

@@ -491,8 +491,11 @@ namespace ExtUI {
   void onLoadSettings(const char*) {}
   void onConfigurationStoreWritten(bool) {}
   void onConfigurationStoreRead(bool) {}
+
+  #if HAS_MESH
     void onMeshUpdate(const int8_t xpos, const int8_t ypos, const float zval) {}
     void onMeshUpdate(const int8_t xpos, const int8_t ypos, const ExtUI::probe_state_t state) {}
+  #endif
 
   #if ENABLED(POWER_LOSS_RECOVERY)
     void onPowerLossResume() {}