doc: remove section on "recent" ECDH changes

The ECDH API changes were made more than six years ago and this
section is not helpful for new applications. The behavior of the ECDH
APIs should be explained in the relevant sections, not in a note.

Refs: nodejs#3511

doc/api/crypto.md

@@ -5464,21 +5464,6 @@ and returned `'latin1'` encoded strings by default rather than `Buffer`s. This
 default was changed after Node.js v0.8 to use [`Buffer`][] objects by default
 instead.
 
-### Recent ECDH changes
-
-Usage of `ECDH` with non-dynamically generated key pairs has been simplified.
-Now, [`ecdh.setPrivateKey()`][] can be called with a preselected private key
-and the associated public point (key) will be computed and stored in the object.
-This allows code to only store and provide the private part of the EC key pair.
-[`ecdh.setPrivateKey()`][] now also validates that the private key is valid for
-the selected curve.
-
-The [`ecdh.setPublicKey()`][] method is now deprecated as its inclusion in the
-API is not useful. Either a previously stored private key should be set, which
-automatically generates the associated public key, or [`ecdh.generateKeys()`][]
-should be called. The main drawback of using [`ecdh.setPublicKey()`][] is that
-it can be used to put the ECDH key pair into an inconsistent state.
-
 ### Support for weak or compromised algorithms
 
 The `crypto` module still supports some algorithms which are already
@@ -6028,7 +6013,6 @@ See the [list of SSL OP Flags][] for details.
 [`diffieHellman.setPublicKey()`]: #diffiehellmansetpublickeypublickey-encoding
 [`ecdh.generateKeys()`]: #ecdhgeneratekeysencoding-format
 [`ecdh.setPrivateKey()`]: #ecdhsetprivatekeyprivatekey-encoding
-[`ecdh.setPublicKey()`]: #ecdhsetpublickeypublickey-encoding
 [`hash.digest()`]: #hashdigestencoding
 [`hash.update()`]: #hashupdatedata-inputencoding
 [`hmac.digest()`]: #hmacdigestencoding