Revert "fs/sync.c: add async_fsync"

This reverts commit 44da06bfa512c7403455986409ef1afe14131436.
Revert "switch do_fsync() to fget_light()"

This reverts commit b6ec26c6949b5e82e291abcdcf9a6dc85f470c7b.
Revert "Revert "Added fsync on/off support.""

This reverts commit 0f69dfc7629b2540cdb6667ae03b0f38f618aa4e.
Revert "Revert "fs: sync: add missing return if fsync is disabled from userspace.""

This reverts commit 353ac8885fe2afc5a96b2d963e7c73a2c49de6c2.
Revert "Revert "fs: sync: enable fsync by default.""

This reverts commit 56809d9b92d96413a536896c8d02550a0a2774c0.