It seems the way to get rid of icons in buttons in GNOME 2.26 has changed.
The line ‘gtk-button-images = 0′ in GTK themes does not work in GNOME 2.26 anymore.
There is now a new key in GNOME Configurator Editor. Below are the steps to disable buttons on icons in GNOME 2.26 and above.
- Press Alt + F2
- Type gconf-editor and hit Enter.
- Go to Desktop –> GNOME –> Interface
- Uncheck the key buttons_have_icons
The change will be immediate and there will no icons on buttons anymore. 
This change will affect all GTK themes. Somehow this is more convenient as I need not edit GTK themes everytime. 