Removed unused file

Author: cpq

steps/step-6-clock/Makefile

@@ -25,10 +25,10 @@ flash: firmware.bin
 	st-flash --reset write $< 0x8000000
 
 cmsis_core:
-	git clone --depth 1 -b 5.9.0 https://github.com/ARM-software/CMSIS_5 $@
+	git clone -q -c advice.detachedHead=false --depth 1 -b 5.9.0 https://github.com/ARM-software/CMSIS_5 $@
 
 cmsis_f4:
-	git clone --depth 1 -b v2.6.8 https://github.com/STMicroelectronics/cmsis_device_f4 $@
+	git clone -q -c advice.detachedHead=false --depth 1 -b v2.6.8 https://github.com/STMicroelectronics/cmsis_device_f4 $@
 
 clean:
 	$(RM) firmware.* cmsis_*