Fixes NB#76638

Fixes NB#76638
I had to remove the menu entry MessageEditWindow->menu->zoom and all of the associated code. I also changed the callback for the HW buttons, so now they show an "Unable to zoom" banner.
Changes:
   * modest/src/widgets/modest-msg-edit-window-ui.h: remove _"Zoom"_ action entries.
   * modest/src/maemo/modest-msg-edit-window.c: remove code associated with the "Zoom" menu entries, use a callback for the HW buttons that only shows a banner.
   * modest/src/maemo/modest-msg-edit-window-ui-dimming.h: remove dimming rules for "Zoom" menu entries.
   * modest/src/maemo/ui/modest-msg-edit-window-ui.xml: remove "Zoom" menu entries.

pmo-trunk-r3797