Remove unused symbol HAVE_BSD_ICONV (#13373)

UPGRADING.INTERNALS

@@ -62,6 +62,7 @@ PHP 8.4 INTERNALS UPGRADE NOTES
      8.0).
    - Symbol DARWIN has been removed (use __APPLE__ to target Darwin systems).
    - Symbol MISSING_FCLOSE_DECL and M4 macro PHP_MISSING_FCLOSE_DECL removed.
+   - Symbol HAVE_BSD_ICONV has been removed.
 
  c. Windows build system changes
    - The configure options --with-oci8-11g, --with-oci8-12c, --with-oci8-19 have

ext/iconv/config.m4

@@ -72,7 +72,6 @@ int main(void) {
         ;;
 
       bsd [)]
-        AC_DEFINE([HAVE_BSD_ICONV],1,[Konstantin Chuguev's iconv implementation])
         AC_DEFINE([PHP_ICONV_IMPL],["BSD iconv"],[Which iconv implementation to use])
         ;;