u-boot: remove extra CFLAGS / LDFLAGS handling

TARGET_CONFIGURE_FLAGS already contain CFLAGS/LDFLAGS, so no point in
setting them explicitly.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

boot/u-boot/u-boot.mk

@@ -129,8 +129,6 @@ endif # BR2_TARGET_UBOOT_NETWORK
 # Build U-Boot itself
 $(U_BOOT_DIR)/$(U_BOOT_BIN): $(U_BOOT_DIR)/.header_modified
 	$(TARGET_CONFIGURE_OPTS) \
-		CFLAGS="$(TARGET_CFLAGS)" \
-		LDFLAGS="$(TARGET_LDFLAGS)" \
 		$(U_BOOT_CONFIGURE_OPTS) \
 		$(MAKE) CROSS_COMPILE="$(CCACHE) $(TARGET_CROSS)" ARCH=$(U_BOOT_ARCH) \
 		$(U_BOOT_MAKE_OPT) -C $(U_BOOT_DIR)