src/lxc/syscall_numbers.h: drop define -1

src/lxc/syscall_numbers.h: drop define -1

Drop "#define -1" to avoid the following m68k build failure with gcc 12:

In file included from ../src/lxc/syscall_wrappers.h:19,
                 from ../src/lxc/mount_utils.h:15,
                 from ../src/lxc/conf.h:24,
                 from ../src/lxc/log.h:19,
                 from ../src/lxc/storage/btrfs.c:20:
../src/lxc/syscall_numbers.h:423:25: error: macro names must be identifiers
  423 |                 #define -1
      |                         ^

Fixes:
 - http://autobuild.buildroot.org/results/f40a517eba86838b11b4b1d6a8a05b8233a3394d

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>