Remove deprecated templates

Several velocity templates haven't been used in a long time (Dodo, a few in Albatross), so they should be removed:

• analytics.vm (there's a new way to enable Google Analytics from the administration)
• changeavatar.vm & changemyavatar.vm (replaced by the new attachment picker)
• diff.vm (an ancient alias of history.vm)
• editmodes.vm (selecting the editor from tabs on top of the edit area)
• flash.vm (never really used)
• languages.vm (no idea)
• menuadmin.vm and menuedit.vm (useless replacements for the top menu, no longer needed)
• save.vm (this one shouldn't ever have been used, since saving redirects to view mode)
• space.vm (replaced by hierarchy.vm)
• viewheader.vm (old Dodo template, replaced by global.vm)