x86/build: Remove unused OBJECT_FILES_NON_STANDARD_test_nx.o

Commit 3ad38ceb ("x86/mm: Remove CONFIG_DEBUG_NX_TEST")
removed arch/x86/kernel/test_nx.c
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220711041247.119357-1-masahiroy@kernel.org

arch/x86/kernel/Makefile

@@ -34,8 +34,6 @@ KASAN_SANITIZE_sev.o					:= n
 # by several compilation units. To be safe, disable all instrumentation.
 KCSAN_SANITIZE := n
 
-OBJECT_FILES_NON_STANDARD_test_nx.o			:= y
-
 # If instrumentation of this dir is enabled, boot hangs during first second.
 # Probably could be more selective here, but note that files related to irqs,
 # boot, dumpstack/stacktrace, etc are either non-interesting or can lead to