Remove bogus notice that older clients might not work with MD5 passwords.

That was written when we still had "crypt" authentication, and it was
referring to the fact that an older client might support "crypt"
authentication but not "md5". But we haven't supported "crypt" for years.
(As soon as we add a new authentication mechanism that doesn't work with
MD5 hashes, we'll need a similar notice again. But this text as it's worded
now is just wrong.)

Backpatch to all supported versions.

Discussion: https://www.postgresql.org/message-id/9a7263eb-0980-2072-4424-440bb2513dc7@iki.fi

doc/src/sgml/ref/create_role.sgml

@@ -235,12 +235,6 @@ CREATE ROLE <replaceable class="PARAMETER">name</replaceable> [ [ WITH ] <replac
         password string).  This allows reloading of encrypted
         passwords during dump/restore.
        </para>
-
-       <para>
-        Note that older clients might lack support for the MD5
-        authentication mechanism that is needed to work with passwords
-        that are stored encrypted.
-       </para>
       </listitem>
      </varlistentry>