package/linux-headers: drop 6.15.x option

The 6.15.x series is now EOL upstream, so drop the linux-headers
option and add legacy handling for it.

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Julien Olivain <ju.o@free.fr>

Config.in.legacy

@@ -146,6 +146,13 @@ endif
 
 comment "Legacy options removed in 2025.08"
 
+config BR2_KERNEL_HEADERS_6_15
+	bool "kernel headers version 6.15.x are no longer supported"
+	select BR2_LEGACY
+	help
+	  Version 6.15.x of the Linux kernel headers are no longer
+	  maintained upstream and are now removed.
+
 config BR2_PACKAGE_LIBCURL_BEARSSL
 	bool "libcurl removed BearSSL support"
 	select BR2_LEGACY

linux/linux.hash

@@ -1,6 +1,5 @@
 # From https://www.kernel.org/pub/linux/kernel/v6.x/sha256sums.asc
 sha256  1a4be2fe6b5246aa4ac8987a8a4af34c42a8dd7d08b46ab48516bcc1befbcd83  linux-6.16.tar.xz
-sha256  e94f3af85492302f7a819441458f80bca0ad9912e5a4c83c699ff3c63c52957d  linux-6.15.9.tar.xz
 sha256  6b19a3ae99423de2416964d67251d745910277af258b4c4c63e88fd87dbf0e27  linux-6.12.41.tar.xz
 sha256  8c4ff2869736538b9b0d88ea8dbf0332b79c6ecc40a32066768a754df1fae1c0  linux-6.6.101.tar.xz
 sha256  218f25663a41e3d811e84fa1c4acec50684898b2f6d0c8c0deb531d937e466f7  linux-6.1.147.tar.xz

package/linux-headers/Config.in.host

@@ -54,10 +54,6 @@ config BR2_KERNEL_HEADERS_6_12
 	bool "Linux 6.12.x kernel headers"
 	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_6_12
 
-config BR2_KERNEL_HEADERS_6_15
-	bool "Linux 6.15.x kernel headers"
-	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_6_15
-
 config BR2_KERNEL_HEADERS_6_16
 	bool "Linux 6.16.x kernel headers"
 	select BR2_TOOLCHAIN_HEADERS_AT_LEAST_6_16
@@ -464,7 +460,6 @@ config BR2_DEFAULT_KERNEL_HEADERS
 	default "6.1.147"	if BR2_KERNEL_HEADERS_6_1
 	default "6.6.101"	if BR2_KERNEL_HEADERS_6_6
 	default "6.12.41"	if BR2_KERNEL_HEADERS_6_12
-	default "6.15.9"	if BR2_KERNEL_HEADERS_6_15
 	default "6.16"		if BR2_KERNEL_HEADERS_6_16
 	default BR2_DEFAULT_KERNEL_VERSION if BR2_KERNEL_HEADERS_VERSION
 	default "custom"	if BR2_KERNEL_HEADERS_CUSTOM_TARBALL