package/linux-headers: drop 4.9.x option

The 4.9.x series is now EOL upstream, so drop the linux-headers option and
add legacy handling for it.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Config.in.legacy

@@ -146,6 +146,13 @@ endif
 
 comment "Legacy options removed in 2023.02"
 
+config BR2_KERNEL_HEADERS_4_9
+	bool "kernel headers version 4.9.x are no longer supported"
+	select BR2_LEGACY
+	help
+	  Version 4.9.x of the Linux kernel headers are no longer
+	  maintained upstream and are now removed.
+
 config BR2_PACKAGE_DOCKER_PROXY
 	bool "docker-proxy removed"
 	select BR2_LEGACY

linux/linux.hash

@@ -6,7 +6,6 @@ sha256  e7ed24f2690bf0e11158ccfa8ddc5c0e8a4816d83c4055d205218853da9c5dad  linux-
 sha256  d807f97812e566410cd13b3170009e0d7552748d4f22d608ffd4dbd7f85bf9c6  linux-5.10.167.tar.xz
 sha256  8dd0ea7f1db4c1e89d485255798e3c3dfb9be63c0f2af369912a1a37b75f36a8  linux-5.4.231.tar.xz
 # From https://www.kernel.org/pub/linux/kernel/v4.x/sha256sums.asc
-sha256  5385aaec55c766e3f462511453f5c63d7898b2d0e9ea74f22a23ebbedab0b3c6  linux-4.9.337.tar.xz
 sha256  a35bcde16b13aa423a1822675775a1b0abf17f5392454febabd8c3757187959a  linux-4.14.305.tar.xz
 sha256  489fb9368bd7ab808264dea1a4acdf607f057bf1ba19f647a17aa18d08f313f9  linux-4.19.272.tar.xz
 # Locally computed

package/linux-headers/Config.in.host

@@ -24,11 +24,6 @@ config BR2_KERNEL_HEADERS_AS_KERNEL
 	depends on BR2_LINUX_KERNEL
 	select BR2_KERNEL_HEADERS_LATEST if BR2_LINUX_KERNEL_LATEST_VERSION
 
-config BR2_KERNEL_HEADERS_4_9
-	bool "Linux 4.9.x kernel headers"
-	depends on !BR2_riscv
-	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_9
-
 config BR2_KERNEL_HEADERS_4_14
 	bool "Linux 4.14.x kernel headers"
 	depends on !BR2_riscv
@@ -393,7 +388,6 @@ endchoice
 
 config BR2_DEFAULT_KERNEL_HEADERS
 	string
-	default "4.9.337"	if BR2_KERNEL_HEADERS_4_9
 	default "4.14.305"	if BR2_KERNEL_HEADERS_4_14
 	default "4.19.272"	if BR2_KERNEL_HEADERS_4_19
 	default "5.4.231"	if BR2_KERNEL_HEADERS_5_4