wmaker.inst: remove all modification to ~/.xinitrc
I cannot imagine that modifying an existing ~/.xinitrc is ever wanted, and creating an ~/.xinitrc when none exists is much worse.
If a user created their own ~/.xinitrc, then don't modify it.
The user will modify it if they like.
If the user did not create their own ~/.xinitrc, then creating one will short-circuit X startup as `startx` will *replace* the system's version with the user's version.
Literally ~/.Xresources won't be loaded.
There's no way this is expected behavior.