tools/unit-test-app: fix build warning

tools/unit-test-app/Makefile

@@ -7,9 +7,6 @@ PROJECT_NAME := unit-test-app
 
 include $(IDF_PATH)/make/project.mk
 
-print_flash_cmd:
-	echo $(ESPTOOL_WRITE_FLASH_OPTIONS) $(ESPTOOL_ALL_FLASH_ARGS) | sed -e 's:'$(PWD)/build/'::g'
-
 # List of unit-test-app configurations.
 # Each file in configs/ directory defines a configuration. The format is the
 # same as sdkconfig file. Configuration is applied on top of sdkconfig.defaults