Looks to be removed by this patch: https://review.dev.storj.io/c/storj/storj/+/16040
Commit message explains the challenges, why it is removed.
Looks like piecestore (and also hashstore) share the information via the prometheus compatible metrics endpoint:
http://localhost:30009/metrics (30009 is my debug port)
blobs_usage{satellite="_12whfK1EDvHJtajBiAUeajQLYcWqxcQmdYQU5zX5cCf6bAxfgu4",scope="storj_io_storj_storagenode_pieces",field="total_size"} 5.791104e+07
blobs_usage{satellite="_12whfK1EDvHJtajBiAUeajQLYcWqxcQmdYQU5zX5cCf6bAxfgu4",scope="storj_io_storj_storagenode_pieces",field="content_size"} 5.788288e+07