Make Block.evidence non-optional in Tendermint client

[webmaster128]

In

export interface Block {
  readonly header: Header;
  /**
   * For the block at height 1, last commit is not set.
   */
  readonly lastCommit: Commit | null;
  readonly txs: readonly Uint8Array[];
  readonly evidence?: readonly Evidence[];
}

the evidence field is always set, even if an empty array. There is no need to differentiate between an empty array and undefined.