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.
Removed call to clear_n_oldest_blocks.
Dropped unused compress_n_oldest_blocks function.
Removed unused get_number_of_log_blocks function.
Removed patch_disk_storage_t::store_patch.
Removed patch_disk_storage_t::load_patches and shutdown.
Removed any semblance that a patch_disk_storage_t would ever be constructed.
Removed unused function patch_memory_storage_t::load_block_patch_list.
Removed patch_memory_storage_t::first_patch.
Added comment noting that patch_map is always empty.
Made apply_patch just ensure_flush all the time, dropped patch_memory_storage_t::store_patch.
Made patch_memory_storage_t assert that patch_map cannot be modified.  It seemingly cannot.
Marked patch_memory_storage_t::patch_map const to convincingly show that it is empty.
Removed calls to patch_memory_storage_t::has_patches_for_block and related calls that are no longer used.
Removed use of apply_patches (which was a nop).