ap51-flash: Remove FLASH_FROM_FILE preprocessor variable

ap51-flash doesn't know the FLASH_FROM_FILE preprocessor variable and thus
OpenWrt should not set it in its package Makefile.

Signed-off-by: Sven Eckelmann <sven@narfation.org>

utils/ap51-flash/Makefile

@@ -27,7 +27,7 @@ define Package/ap51-flash
   URL:=http://dev.cloudtrax.com/wiki/ap51-flash-station
 endef
 
-TARGET_EXTRA_CFLAGS:=-DFLASH_FROM_FILE -D_GNU_SOURCE
+TARGET_EXTRA_CFLAGS:=-D_GNU_SOURCE
 
 # pass optimization flags
 MAKE_FLAGS += \