[glibmm] Doxyfile.in: Remove obsolete entry

[Kjell Ahlstedt <kjellahl src gnome org>]

commit e3fe24233ffb2a8797e2dbf055004090ea7d70f2
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Mon Aug 22 13:27:43 2022 +0200

    Doxyfile.in: Remove obsolete entry

 docs/reference/Doxyfile.in | 1 -
 1 file changed, 1 deletion(-)
---
diff --git a/docs/reference/Doxyfile.in b/docs/reference/Doxyfile.in
index 9a1e6d57..ed48e2a4 100644
--- a/docs/reference/Doxyfile.in
+++ b/docs/reference/Doxyfile.in
@@ -158,7 +158,6 @@ CLANG_OPTIONS          =
 # Configuration options related to the alphabetical class index
 #---------------------------------------------------------------------------
 ALPHABETICAL_INDEX     = YES
-COLS_IN_ALPHA_INDEX    = 5
 IGNORE_PREFIX          =
 #---------------------------------------------------------------------------
 # Configuration options related to the HTML output