[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`)
- [x] remove references to easy mode from the documentation
- [x] update man pages.
- [ ] translations (I need some hints on how to proceed here).
To clarify, I don't mind updating my changes after this is merged.