specs: remove evidence

[rootulp]

#950 failed to account for updating the specs after removing evidence from the data square. In particular the following instances need to be removed:

1. celestia-app/specs/src/specs/consensus.md

   Line 18 in 329dc50

   - [`block.availableData.evidenceData`](#blockavailabledataevidencedata)

2. celestia-app/specs/src/rationale/message_block_layout.md

   Line 14 in 329dc50

   Block data consists of transactions (which modify the Celestia chain's state), intermediate state roots (required for fraud proofs of the aforementioned transactions), messages (binary blobs which do not modify the Celestia state, but which are intended for a Celestia application identified with a provided namespace ID), and other relevant pieces of data (e.g. evidence for slashing). We want to arrange this data into a `k * k` matrix of fixed-sized shares, which will later be committed to in [Namespace Merkle Trees (NMTs)](../specs/data_structures.md#namespace-merkle-tree).

3. celestia-app/specs/src/specs/data_structures.md

   Lines 819 to 858 in 329dc50

   	### EvidenceData
   	Wrapper for evidence data.
   	| name | type | description |
   	|-------------|---------------------------|------------------------------------------------|
   	| `evidences` | [Evidence](#evidence)`[]` | List of evidence used for slashing conditions. |
   	#### Evidence
   	| name | type | description |
   	|----------|-------------------------|-------------|
   	| `pubKey` | [PublicKey](#publickey) | |
   	| `voteA` | [Vote](#vote) | |
   	| `voteB` | [Vote](#vote) | |
   	#### PublicKey
   	| name | type | description |
   	|------|------------|--------------------------|
   	| `x` | `byte[32]` | `x` value of public key. |
   	| `y` | `byte[32]` | `y` value of public key. |
   	#### Vote
   	```C++
   	enum VoteType : uint8_t {
   	Prevote = 1,
   	Precommit = 2,
   	};
   	```
   	| name | type | description |
   	|--------------|---------------------------|-------------|
   	| `type` | `VoteType` | |
   	| `height` | [Height](#type-aliases) | |
   	| `round` | [Round](#type-aliases) | |
   	| `headerHash` | [HashDigest](#hashdigest) | |
   	| `timestamp` | [Timestamp](#timestamp) | |
   	| `signature` | [Signature](#signature) | |

[rootulp]

Closed by #1436