chore: remove old snapshots

These old snapshots are affected by a `pathfinder` bug and should no
longer be used:

    https://github.com/eqlabs/pathfinder/releases/tag/v0.6.7

README.md

@@ -49,24 +49,15 @@ tar Jxvf ./mainnet-v0.7.0-141083.tar.xz
 | Network   | Version  | Block    | Download Link                                                             |
 | --------- | -------- | -------- | ------------------------------------------------------------------------- |
 | `mainnet` | `v0.7.0` | `141083` | https://pathfinder-backup.zklend.com/mainnet/mainnet-v0.7.0-141083.tar.xz |
-| `mainnet` | `v0.6.3` | `98021`  | https://pathfinder-backup.zklend.com/mainnet/mainnet-v0.6.3-98021.tar.xz  |
-| `mainnet` | `v0.5.6` | `64152`  | https://pathfinder-backup.zklend.com/mainnet/mainnet-v0.5.6-64152.tar.xz  |
-| `mainnet` | `v0.5.4` | `56215`  | https://pathfinder-backup.zklend.com/mainnet/mainnet-56215.tar.xz         |
 
 ### `goerli-1`
 
 | Network    | Version  | Block    | Download Link                                                               |
 | ---------- | -------- | -------- | --------------------------------------------------------------------------- |
 | `goerli-1` | `v0.7.0` | `841817` | https://pathfinder-backup.zklend.com/goerli-1/goerli-1-v0.7.0-841817.tar.xz |
-| `goerli-1` | `v0.6.3` | `827907` | https://pathfinder-backup.zklend.com/goerli-1/goerli-1-v0.6.3-827907.tar.xz |
-| `goerli-1` | `v0.5.6` | `810033` | https://pathfinder-backup.zklend.com/goerli-1/goerli-1-v0.5.6-810033.tar.xz |
-| `goerli-1` | `v0.5.4` | `806055` | https://pathfinder-backup.zklend.com/goerli-1/goerli-1-806055.tar.xz        |
 
 ### `goerli-2`
 
 | Network    | Version  | Block    | Download Link                                                               |
 | ---------- | -------- | -------- | --------------------------------------------------------------------------- |
 | `goerli-2` | `v0.7.0` | `136651` | https://pathfinder-backup.zklend.com/goerli-2/goerli-2-v0.7.0-136651.tar.xz |
-| `goerli-2` | `v0.6.3` | `123022` | https://pathfinder-backup.zklend.com/goerli-2/goerli-2-v0.6.3-123022.tar.xz |
-| `goerli-2` | `v0.5.6` | `113175` | https://pathfinder-backup.zklend.com/goerli-2/goerli-2-v0.5.6-113175.tar.xz |
-| `goerli-2` | `v0.5.4` | `110568` | https://pathfinder-backup.zklend.com/goerli-2/goerli-2-110568.tar.xz        |