[conf] removed AHRS_MAG_UPDATE_YAW_ONLY from some imu subsystem makefiles, does not exist anymore

* print an error when trying to use the imu aspirin (SPI) subsystems with the lpc

conf/firmwares/subsystems/fixedwing/imu_aspirin2_i2c.makefile

@@ -18,6 +18,3 @@ endif
 
 ap.CFLAGS += $(IMU_ASPIRIN2_CFLAGS)
 ap.srcs   += $(IMU_ASPIRIN2_SRCS)
-
-ap.CFLAGS += -DAHRS_MAG_UPDATE_YAW_ONLY
-

conf/firmwares/subsystems/fixedwing/imu_ppzuav.makefile

@@ -18,6 +18,3 @@ endif
 
 ap.CFLAGS += $(IMU_PPZUAV_CFLAGS)
 ap.srcs   += $(IMU_PPZUAV_SRCS)
-
-ap.CFLAGS += -DAHRS_MAG_UPDATE_YAW_ONLY
-

conf/firmwares/subsystems/shared/imu_aspirin_common.makefile

@@ -52,7 +52,7 @@ IMU_ASPIRIN_SRCS   += peripherals/hmc5843.c $(SRC_ARCH)/peripherals/hmc5843_arch
 IMU_ASPIRIN_CFLAGS += -DUSE_I2C2
 
 ifeq ($(ARCH), lpc21)
-#TODO
+$(error The aspirin subsystem (using SPI) is currently not implemnented for the lpc21. Please use the aspirin_i2c subsystem.)
 else ifeq ($(ARCH), stm32)
 IMU_ASPIRIN_CFLAGS += -DUSE_EXTI15_10_IRQ  # Gyro Int on PC14
 IMU_ASPIRIN_CFLAGS += -DUSE_EXTI9_5_IRQ    # Mag Int on PB5