Remove atomicity warning that does not apply to STM32

Signed-off-by: Taylor Braun-Jones <[email protected]>

Author: nocnokneo

Diff for: cores/arduino/HardwareSerial.h

@@ -35,11 +35,6 @@
 // location from which to read.
 // NOTE: a "power of 2" buffer size is recommended to dramatically
 //       optimize all the modulo operations for ring buffers.
-// WARNING: When buffer sizes are increased to > 256, the buffer index
-// variables are automatically increased in size, but the extra
-// atomicity guards needed for that are not implemented. This will
-// often work, but occasionally a race condition can occur that makes
-// Serial behave erratically. See https://github.com/arduino/Arduino/issues/2405
 #if !defined(SERIAL_TX_BUFFER_SIZE)
   #define SERIAL_TX_BUFFER_SIZE 64
 #endif