Always exclude range test

Range test is excluded on every target as of 2.8, so set
MESHTASTIC_EXCLUDE_RANGETEST=1 globally in [env] build_flags and drop the
now-redundant per-variant flags from esp32, rak11200 and stm32.

Guard RangeTestModule.cpp with the same condition used in Modules.cpp so the
translation unit compiles to nothing rather than relying on --gc-sections to
strip it, and always report RANGETEST_CONFIG in the device metadata
excluded_modules bitmask so clients hide the config.

src/main.cpp

@@ -1279,6 +1279,8 @@ extern meshtastic_DeviceMetadata getDeviceMetadata()
 #if !defined(HAS_RGB_LED) && !RAK_4631
     deviceMetadata.excluded_modules |= meshtastic_ExcludedModules_AMBIENTLIGHTING_CONFIG;
 #endif
+    // Range test is always excluded as of 2.8
+    deviceMetadata.excluded_modules |= meshtastic_ExcludedModules_RANGETEST_CONFIG;
 
 // No bluetooth on these targets (yet):
 // Pico W / 2W may get it at some point