[SDK] Remove `gasPrice` from `Transaction` type


as a field is getting deprecated from the backend we should update the SDK to match the response  from a backend
https://github.com/ChainSafe/sprinter-api/issues/284#issue-2591869900

https://github.com/ChainSafe/sprinter-ts/blob/cca32fe1c2bc4cc8c6b15ca12b00ac4c87874f8b/packages/sdk/src/types.ts#L104