Revert "ext4: speed up truncate/unlink by not using bforget() unless needed"

This reverts commit 38f382845b2c9acd92ae82400b9372d0a20ba9c8.
Revert "ext4: Speedup WB_SYNC_ALL pass called from sync(2)"

This reverts commit 54b3cd25f6c1da21d48c1d07d49ca91536afe0fa.