Revert "Clarify documentation for the initcap function"

This reverts commit 1fe9e3822c.  That commit
was a documentation improvement, not a bug fix.  We don't normally backpatch
such changes.

Discussion: https://postgr.es/m/d8eacbeb8194c578a98317b86d7eb2ef0b6eb0e0.camel%40j-davis.com

doc/src/sgml/func.sgml

@@ -3049,11 +3049,8 @@ repeat('Pg', 4) <returnvalue>PgPgPgPg</returnvalue>
        </para>
        <para>
         Converts the first letter of each word to upper case and the
-        rest to lower case. When using the <literal>libc</literal> locale
-        provider, words are sequences of alphanumeric characters separated
-        by non-alphanumeric characters; when using the ICU locale provider,
-        words are separated according to
-        <ulink url="https://www.unicode.org/reports/tr29/#Word_Boundaries">Unicode Standard Annex #29</ulink>.
+        rest to lower case. Words are sequences of alphanumeric
+        characters separated by non-alphanumeric characters.
        </para>
        <para>
         <literal>initcap('hi THOMAS')</literal>