Removed pointless typedefs in writeback.hpp.
Patch storage removal: Pinned patch_disk_storage_t::number_of_blocks to 0.
Patch storage removal: Removed swathes of code made dead by setting number_of_blocks to 0.
Patch storage removal: Removed now-unused functions in patch_disk_storage_t.
Patch storage removal: Removed patch_disk_storage_t::block_is_empty and log_block_bufs.
Patch storage removal: Removed all patch_disk_storage_t variables.