Removing super_block flags

When removing all the code for stable pages for direct IO writes for
Linux I forgot to remove the flags for the struct super_block. This
should have be removed previously. Now all code related to trying to get
stable pages on the Linux side should be completely removed from the
code.

Signed-off-by: Brian Atkinson <batkinson@lanl.gov>

module/os/linux/zfs/zfs_vfsops.c

@@ -1533,12 +1533,6 @@ zfs_domount(struct super_block *sb, zfs_mnt_t *zm, int silent)
 
 	sb->s_bdi->ra_pages = 0;
 
-#if defined(SB_I_STABLE_WRITES)
-	sb->s_iflags |= SB_I_STABLE_WRITES;
-#elif defined(BDI_CAP_STABLE_WRITES)
-	sb->s_bdi->capabilities |= BDI_CAP_STABLE_WRITES;
-#endif
-
 	/* Set callback operations for the file system. */
 	sb->s_op = &zpl_super_operations;
 	sb->s_xattr = zpl_xattr_handlers;