Remove KERN_STACKTOP

It got removed by upstream.  This should not be considered a breaking
change, because KERN_STACKTOP has never been included in a released
version of FreeBSD.

freebsd/freebsd-src@1544f5a

Author: asomers

libc-test/build.rs

@@ -2091,8 +2091,6 @@ fn test_freebsd(target: &str) {
 
             "VM_TOTAL" if Some(11) == freebsd_ver => true,
 
-            // Added in FreeBSD 14.
-            "KERN_STACKTOP" if Some(14) > freebsd_ver => true,
             // Added in FreeBSD 13.
             "KERN_PROC_SIGFASTBLK"
             | "USER_LOCALBASE"

src/unix/bsd/freebsdlike/freebsd/mod.rs

@@ -2056,7 +2056,6 @@ pub const KERN_IOV_MAX: ::c_int = 35;
 pub const KERN_HOSTUUID: ::c_int = 36;
 pub const KERN_ARND: ::c_int = 37;
 pub const KERN_MAXPHYS: ::c_int = 38;
-pub const KERN_STACKTOP: ::c_int = 39;
 
 pub const KERN_PROC_ALL: ::c_int = 0;
 pub const KERN_PROC_PID: ::c_int = 1;