boot/uboot: remove use of legacy xloader symbol

Commit "070b183d0c boot/xloader: remove package", from release 2018.11,
removed the package, but the symbol is still referenced.

Remove the reference to it.

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/uboot/Config.in

@@ -450,7 +450,6 @@ endif
 
 config BR2_TARGET_UBOOT_SPL
 	bool "Install U-Boot SPL binary image"
-	depends on !BR2_TARGET_XLOADER
 	help
 	  Install the U-Boot SPL binary image to the images
 	  directory.