Simplify "ensure" phrasing.

- delete now-errant line

- fix "ensure" phrasing — note: this sentence may need further work, as it's not clear whether confirming `an array of five elements` is sufficient to populate `the five elements` --
  ```
  Initialize |components| to an array that is the result of CBOR-decoding the
  bytes that follow the three-byte ECDSA-SD base proof header. Ensure the result
  is an array of five elements.
              </li>
              <li>
  Return an object with properties set to the five elements, using the names
  `baseSignature`, `publicKey`, `hmacKey`, `signatures`, and `mandatoryPointers`,
  respectively.
  ```

index.html

@@ -2249,7 +2249,7 @@ <h4>parseBaseProofValue</h4>
             </li>
             <li>
 Initialize |components| to an array that is the result of CBOR-decoding the
-bytes that follow the three-byte ECDSA-SD base proof header. Ensure the result
+bytes that follow the three-byte ECDSA-SD base proof header. Confirm that the result
 is an array of five elements.
             </li>
             <li>
@@ -2507,7 +2507,6 @@ <h4>parseDerivedProofValue</h4>
 
           <ol class="algorithm">
             <li>
-Ensure the |proofValue| string starts with `u`, indicating that it is a
 If the |proofValue| string does not start with `u`, indicating that it is a
 multibase-base64url-no-pad-encoded value, an error MUST be raised
 and SHOULD convey an error type of