[mutter] tests/monitor-test-utils: Remove unused function definition

[Jonas Ådahl <jadahl src gnome org>]

commit f3a65c9b32229d8b5d17968ca96394dd64cabfa1
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Fri May 8 20:55:12 2020 +0200

    tests/monitor-test-utils: Remove unused function definition
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1243

 src/tests/monitor-test-utils.h | 2 --
 1 file changed, 2 deletions(-)
---
diff --git a/src/tests/monitor-test-utils.h b/src/tests/monitor-test-utils.h
index 4b9b3f0c7..0b0dc6d7d 100644
--- a/src/tests/monitor-test-utils.h
+++ b/src/tests/monitor-test-utils.h
@@ -22,8 +22,6 @@
 
 #include <glib.h>
 
-gboolean is_using_monitor_config_manager (void);
-
 void set_custom_monitor_config (const char *filename);
 
 char * read_file (const char *file_path);