gitk: Update msgid's for menu items with accelerator

gitk: Update msgid's for menu items with accelerator

The commit d99b4b0de27a ("gitk: Accelerators for the main menu")
modified the menu item strings with the accelerator, but the
translations didn't follow, thus the menus are shown without
translations.

This patch systematically update the msgid keys just to follow this
change.  The contents aren't changed, so the accelerator won't work in
these locales for now.  Each locale translator needs to add proper
acceleration keys appropriately.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>