[WIP] Remove/simplify #ifdefs on default features

Many vim features now is on by default.
Simplest cases like ```#ifdef FEAT_*``` were removed automatically.
In this PR I want to remove all remaining complex ```#ifdef```s which use "default features".
I checked original vim source and all these features were enabled by some things like ```FEAT_NORMAL``` and ```FEAT_BIG``` which are used to define feature richness. As I suppose neovim going to provide all these features by default.