package/libsepol: drop bogus BR2_TOOLCHAIN_HEADERS_AT_LEAST_2_6

The inexistent symbol is reference since this commit from 2020:
'55784bcbfa package/libsepol: set default policy version'

Cc: Clayton Shotwell <clayton.shotwell@collins.com>
Cc: Marcus Folkesson <marcus.folkesson@gmail.com>
Cc: Matt Weber <matthew.weber@collins.com>
Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/libsepol/Config.in

@@ -18,7 +18,6 @@ config BR2_PACKAGE_LIBSEPOL_POLICY_VERSION
 	default 30 if BR2_TOOLCHAIN_HEADERS_AT_LEAST_4_3
 	default 29 if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_14
 	default 28 if BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_5
-	default 26 if BR2_TOOLCHAIN_HEADERS_AT_LEAST_2_6
 	default 25
 	help
 	  The maximum SELinux policy version your kernel supports.