Revert "fuse: add support of async IO && enable asynchronous processing direct IO"

This reverts commit 7aed83d5cbe007f564872f0c317e81aafd943ee5.
Revert "sync: don't block the flusher thread waiting on IO"

This reverts commit c22430fe5715525eceff448073447376065d8ba8.
cflags once again
Merge commit '66229e4' into MAD-2.1