doc: Fix description of configure --with-icu option

It was claiming that the ICU locale provider is used by default, which
is not correct.  (From commit fcb21b3; it was once contemplated to
make it the default, but it wouldn't have been part of that patch in
any case.)

Reviewed-by: Kashif Zeeshan <kashi.zeeshan@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/a71023c2-0ae0-45ad-9688-cf3b93d0d65b%40eisentraut.org

Author: petere

doc/src/sgml/installation.sgml

@@ -167,7 +167,7 @@
 
     <listitem>
      <para>
-      The ICU locale provider (see <xref linkend="locale-providers"/>) is used by default. If you don't want to use it then you must specify the <option>--without-icu</option> option to <filename>configure</filename>. Using this option disables support for ICU collation features (see <xref linkend="collation"/>).
+      The ICU library is used by default. If you don't want to use it then you must specify the <option>--without-icu</option> option to <filename>configure</filename>. Using this option disables support for ICU collation features (see <xref linkend="collation"/>).
      </para>
      <para>
       ICU support requires the <productname>ICU4C</productname> package to be