doc: mark the callback argument of crypto.generatePrime as mandatory

The current documentation lists the `callback` argument of
`crypto.generatePrime` as optional (it's surrounded by square
brackets), but this is incorrect - calling the function without a
callback will result in an `ERR_INVALID_ARG_TYPE` error:

For the record, the correct way to generate a prime synchronously,
without a callback, is to use the `generatePrimeSync` API.

This patch fixes the documentation and marks the callback argument as
mandatory. The `options` (second) argument, is indeed optional, and
is marked as such.

Fixes: #58298

Author: mureinik

doc/api/crypto.md

@@ -3900,7 +3900,7 @@ console.log(key.export().toString('hex'));  // e89..........41e
 The size of a generated HMAC key should not exceed the block size of the
 underlying hash function. See [`crypto.createHmac()`][] for more information.
 
-### `crypto.generatePrime(size[, options[, callback]])`
+### `crypto.generatePrime(size[, options], callback)`
 
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