Gitaly has recently deprecated both the GetLFSPointers and
GetAllLFSPointers RPCs in favor of ListLFSPointers, which is a more
flexible variant which simply takes a list of revisions (including
the pseudo-revs `--not` and `--all`) and then returns all LFS pointers
reachable via these revisions.

Convert the `BlobService::get_new_lfs_pointers` and
`BlobService::get_all_lfs_pointers` RPCs to use the new RPC.