ext4: get rid of unused DEFAULT_MB_OPTIMIZE_SCAN

After recent changes to the mb_optimize_scan mount option
the DEFAULT_MB_OPTIMIZE_SCAN is no longer needed so get
rid of it.
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/20220315114454.104182-1-ojaswin@linux.ibm.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/super.c

@@ -1867,7 +1867,6 @@ static const struct fs_parameter_spec ext4_param_specs[] = {
 };
 
 #define DEFAULT_JOURNAL_IOPRIO (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 3))
-#define DEFAULT_MB_OPTIMIZE_SCAN	(-1)
 
 static const char deprecated_msg[] =
 	"Mount option \"%s\" will be removed by %s\n"