[glibmm] Remove HACKING

[Kjell Ahlstedt <kjellahl src gnome org>]

commit 9c0b7ab4269fa619deb78cf16875eab851c6b2ec
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Mon Feb 14 11:19:11 2022 +0100

    Remove HACKING

 HACKING     | 12 ------------
 meson.build |  3 +--
 2 files changed, 1 insertion(+), 14 deletions(-)
---
diff --git a/meson.build b/meson.build
index 0c39d85e..202b1949 100644
--- a/meson.build
+++ b/meson.build
@@ -273,9 +273,8 @@ if can_add_dist_script
     project_source_root,
   )
 
-  # Don't distribute these files.
+  # Don't distribute this file.
   dont_distribute = [
-    'HACKING',
     '.gitlab-ci.yml',
   ]
   # Add build scripts to the distribution directory, and delete .gitignore