efi: Drop preprocessor directives from zboot.lds

Older versions of `ld` don't seem to support preprocessor directives in
linker scripts, e.g. on RHEL9's ld-2.35.2-63.el9 the build fails with:

 ld:./drivers/firmware/efi/libstub/zboot.lds:32: ignoring invalid character `#' in expression
 ld:./drivers/firmware/efi/libstub/zboot.lds:33: syntax error

We don't seem to need these '#ifdef', no empty .sbat section is created
when CONFIG_EFI_SBAT_FILE="":

 # objdump -h arch/arm64/boot/vmlinuz.efi

 arch/arm64/boot/vmlinuz.efi:     file format pei-aarch64-little

 Sections:
 Idx Name          Size      VMA               LMA               File off  Algn
   0 .text         00b94000  0000000000001000  0000000000001000  00001000  2**2
                   CONTENTS, ALLOC, LOAD, READONLY, CODE
   1 .data         00000200  0000000000b95000  0000000000b95000  00b95000  2**2
                   CONTENTS, ALLOC, LOAD, DATA

Fixes: 0f9a1739 ("efi: zboot specific mechanism for embedding SBAT section")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>