Revert "x86/kexec: add a sanity check on previous kernel's ima kexec buffer"

This reverts commit c5489d0.

The commit introduces a call to ima_validate_range() in
arch/x86/kernel/setup.c, but the function declaration is not available
in the 6.12 stable tree, resulting in build failures due to implicit
function declaration errors across multiple stable branches.

Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Sasha Levin

arch/x86/kernel/setup.c

@@ -372,15 +372,9 @@ int __init ima_free_kexec_buffer(void)
 
 int __init ima_get_kexec_buffer(void **addr, size_t *size)
 {
-	int ret;
-
 	if (!ima_kexec_buffer_size)
 		return -ENOENT;
 
-	ret = ima_validate_range(ima_kexec_buffer_phys, ima_kexec_buffer_size);
-	if (ret)
-		return ret;
-
 	*addr = __va(ima_kexec_buffer_phys);
 	*size = ima_kexec_buffer_size;