ARDUINO_ARCH_STM32 should not be defined

The ARDUINO_ARCH_{build.arch} is used to differentiate core.
See: https://github.com/arduino/Arduino/wiki/Arduino-IDE-1.5:-Library-specification#working-with-multiple-architectures

Defining ARDUINO_ARCH_STM32 will raised several issues on library
supporting both cores:
 * ARDUINO_ARCH_STM32
 * ARDUINO_ARCH_STM32F1

Signed-off-by: Frederic Pillon <[email protected]>

Author: fpistm

STM32F1/platform.txt

@@ -36,7 +36,7 @@ compiler.define=-DARDUINO=
 # this can be overriden in boards.txt
 build.f_cpu=72000000L
 build.mcu=cortex-m3
-build.common_flags=-mthumb  -march=armv7-m -D__STM32F1__ -DARDUINO_ARCH_STM32
+build.common_flags=-mthumb  -march=armv7-m -D__STM32F1__
 build.variant_system_lib=libmaple.a
 ## LED stuff is not really used but is still required in the code
 build.error_led_port=GPIOB