fix(rmt): error case

Author: SuGlider

Diff for: libraries/ESP32/examples/RMT/Legacy_RMT_Driver_Compatible/Legacy_RMT_Driver_Compatible.ino

@@ -10,15 +10,9 @@
 #ifndef ESP32_ARDUINO_NO_RGB_BUILTIN
 
 // add the file "build_opt.h" to your Arduino project folder with "-DESP32_ARDUINO_NO_RGB_BUILTIN" to use the RMT Legacy driver
-#warning "ESP32_ARDUINO_NO_RGB_BUILTIN is not defined, this example is intended to demonstrate the RMT Legacy driver.
-#warning "Please add the file 'build_opt.h' with '-DESP32_ARDUINO_NO_RGB_BUILTIN' to your Arduino project folder."
-#warning "Another way to disable the RGB_BUILTIN is to define it in the platformio.ini file, for instance: '-D ESP32_ARDUINO_NO_RGB_BUILTIN'"
-
-void setup() {
-}
-
-void loop() {
-}
+#error "ESP32_ARDUINO_NO_RGB_BUILTIN is not defined, this example is intended to demonstrate the RMT Legacy driver.
+#error "Please add the file 'build_opt.h' with '-DESP32_ARDUINO_NO_RGB_BUILTIN' to your Arduino project folder."
+#error "Another way to disable the RGB_BUILTIN is to define it in the platformio.ini file, for instance: '-D ESP32_ARDUINO_NO_RGB_BUILTIN'"
 
 #else