[block] remove flush() method

block.h

@@ -149,12 +149,6 @@ namespace persistent_data {
 					  typename validator::ptr v =
 					  typename validator::ptr(new noop_validator()));
 
-		// If you aren't using a superblock, then this flush method
-		// will write all dirty data.  Throws if any locks are
-		// held.
-		// FIXME: do we need this?
-		void flush();
-
 		block_address get_nr_blocks() const;
 
 	private:

block.tcc

@@ -157,15 +157,6 @@ block_manager<BlockSize>::superblock_zero(block_address location,
 	return write_ref(b);
 }
 
-template <uint32_t BlockSize>
-void
-block_manager<BlockSize>::flush()
-{
-	if (lock_count_ > 0)
-		throw runtime_error("asked to flush while locks are still held");
-	::fsync(fd_);
-}
-
 template <uint32_t BlockSize>
 void
 block_manager<BlockSize>::read_buffer(block_address b, block_manager<BlockSize>::buffer &buffer) const