khugepaged: selftests: remove debug_cow

The debug_cow attribute had been removed since commit 4958e4d86ecb01 ("mm:
thp: remove debug_cow switch"), so remove it in selftest code too,
otherwise the khugepaged test will fail.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 4958e4d86ecb01 ("mm: thp: remove debug_cow switch")
Signed-off-by: Nanyong Sun <[e-mail]>
Cc: Yang Shi <[e-mail]>
Cc: Zi Yan <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Kefeng Wang <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

tools/testing/selftests/vm/khugepaged.c

···
 	enum thp_enabled thp_enabled;
 	enum thp_defrag thp_defrag;
 	enum shmem_enabled shmem_enabled;
-	bool debug_cow;
 	bool use_zero_page;
 	struct khugepaged_settings khugepaged;
 };
···
 	.thp_enabled = THP_MADVISE,
 	.thp_defrag = THP_DEFRAG_ALWAYS,
 	.shmem_enabled = SHMEM_NEVER,
-	.debug_cow = 0,
 	.use_zero_page = 0,
 	.khugepaged = {
 		.defrag = 1,
···
 	write_string("defrag", thp_defrag_strings[settings->thp_defrag]);
 	write_string("shmem_enabled",
 			shmem_enabled_strings[settings->shmem_enabled]);
-	write_num("debug_cow", settings->debug_cow);
 	write_num("use_zero_page", settings->use_zero_page);
 
 	write_num("khugepaged/defrag", khugepaged->defrag);
···
 		.thp_defrag = read_string("defrag", thp_defrag_strings),
 		.shmem_enabled =
 			read_string("shmem_enabled", shmem_enabled_strings),
-		.debug_cow = read_num("debug_cow"),
 		.use_zero_page = read_num("use_zero_page"),
 	};
 	saved_settings.khugepaged = (struct khugepaged_settings) {