[WIP] Remove "easy" mode.

This removes vim's "easy" mode, as discussed in issue #1646:

- [x] remove the `-y` argument ("why" indeed)
- [x] remove support for evim and eview aliases
- [x] remove supporting files (`runtime/evim.vim`)
- [ ] remove references to easy mode from the documentation (I thing I got them all, but I'll re-check)
- [ ] update man pages.
- [ ] translations (I need some hints on how to proceed here).