Pod: Having multiple token drops is inconsistent
The `Pod` contract had the `drop` storage field and mapping of different TokenDrops `(token => TokenDrop)`. When adding a new `TokenDrop` in the mapping, the `drop` field is also changed to the added _tokenDrop:\\n```\\nfunction setTokenDrop(address \\_token, address \\_tokenDrop)\\n    external\\n    returns (bool)\\n{\\n    require(\\n        msg.sender == factory || msg.sender == owner(),\\n        "Pod:unauthorized-set-token-drop"\\n    );\\n\\n    // Check if target<>tokenDrop mapping exists\\n    require(\\n        drops[\\_token] == TokenDrop(0),\\n        "Pod:target-tokendrop-mapping-exists"\\n    );\\n\\n    // Set TokenDrop Referance\\n    drop = TokenDrop(\\_tokenDrop);\\n\\n    // Set target<>tokenDrop mapping\\n    drops[\\_token] = drop;\\n\\n    return true;\\n}\\n```\\n\\nOn the other hand, the `measure` token and the `asset` token of the `drop` are strictly defined by the Pod contract. They cannot be changed, so all `TokenDrops` are supposed to have the same `asset` and `measure` tokens. So it is useless to have different `TokenDrops`.
The mapping seems to be unused, and only one `TokenDrop` will normally be in the system. If that code is not used, it should be deleted.
```\\nfunction setTokenDrop(address \\_token, address \\_tokenDrop)\\n    external\\n    returns (bool)\\n{\\n    require(\\n        msg.sender == factory || msg.sender == owner(),\\n        "Pod:unauthorized-set-token-drop"\\n    );\\n\\n    // Check if target<>tokenDrop mapping exists\\n    require(\\n        drops[\\_token] == TokenDrop(0),\\n        "Pod:target-tokendrop-mapping-exists"\\n    );\\n\\n    // Set TokenDrop Referance\\n    drop = TokenDrop(\\_tokenDrop);\\n\\n    // Set target<>tokenDrop mapping\\n    drops[\\_token] = drop;\\n\\n    return true;\\n}\\n```\\n