doc: Fix description of SQL standard parts

The splitting into parts actually started earlier than the text had
claimed, but that is ancient history anyway by now and does not need
to be mentioned.  Update that and tweak the text a bit.

doc/src/sgml/features.sgml

@@ -48,10 +48,8 @@
  </para>
 
  <para>
-  The standard versions beginning with <acronym>SQL:2003</acronym>
-  are also split into a number
-  of parts.  Each is known by a shorthand name.  Note that these parts
-  are not consecutively numbered.
+  The standard is split into a number of parts, each also known by a shorthand
+  name:
 
   <itemizedlist>
    <listitem><para>ISO/IEC 9075-1 Framework (SQL/Framework)</para><indexterm><primary>SQL/Framework</primary></indexterm></listitem>
@@ -65,6 +63,8 @@
    <listitem><para>ISO/IEC 9075-14 XML-related specifications (SQL/XML)</para><indexterm><primary>SQL/XML</primary></indexterm></listitem>
    <listitem><para>ISO/IEC 9075-15 Multi-dimensional arrays (SQL/MDA)</para><indexterm><primary>SQL/MDA</primary></indexterm></listitem>
   </itemizedlist>
+
+  Note that some part numbers are not (or no longer) used.
  </para>
 
  <para>