F2FS_SET_FEATURE() and F2FS_CLEAR_FEATURE() have never
been used since they were introduced by this commit
76f105a2dbcd("f2fs: add feature facility in superblock").
So let's remove them. BTW, convert f2fs_sb_has_##name to return bool.
Signed-off-by: Yangtao Li <frank.li@xxxxxxxx>