You'll need to recompile
gvim to remove the requirement. It's configurable when building it.
This post I wrote on my blog shows how to compile Ruby support in, but you could just as easily remove it. NOTE: this post is Fedora/RHEL specific so it's not a template of steps for you to follow, but just to show you that it is possible to recompile
gvim with/without Ruby support if you so choose.
Incidentally I think the issue you're running into is that the package manger knows that
gvim "requires" and is enforcing this when you try to remove it.
You could override the package manager and "force" the removal if you know no other packages require it.
A 3rd options would be to install the Ruby package, and RVM. When you setup RVM you're overriding your $PATH, so RVM's versions of Ruby are the precedent, even though you have Ruby installed as a package on the system.
So your RVM's Ruby should be the one that
gvim is using anyways.
$ echo $PATH
$ which ruby
Here you can see that when
ruby is invoked, my RVM version is the one getting picked up. Unless
vim/gvim has the path to
ruby hardcoded (I doubt this) then it's bound by the same search through your
$PATH, so it will find the RVM ruby too.