kernel: drop unneeded kernel version dependency

The current master only supports kernel 5.4, and there is no reason
to remove KERNEL_IO_URING for future kernels.

Drop the unneeded dependency.

Signed-off-by: Andy Walsh <andy.walsh44+github@gmail.com>
[improve commit title/message]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

config/Config-kernel.in

@@ -380,7 +380,6 @@ config KERNEL_AIO
 config KERNEL_IO_URING
 	bool "Compile the kernel with io_uring support"
 	default y if !SMALL_FLASH
-	depends on LINUX_5_4
 
 config KERNEL_FHANDLE
 	bool "Compile the kernel with support for fhandle syscalls"