Remove colorcolumn setting from Vim runtime files

[hoelzro]

I think settings like this should be left up to the user.

[bstrie]

We talked about this a bit and I think this is the correct course of action. I originally put in the colorcolumn rule because our original convention of 78 columns was shorter than the typical users' worst-case column length (80), and also because it was short enough that people were hitting it constantly. Now that we've increased the convention to 100 columns, the complaints of hitting the line-length limit during make check have all but vanished, which leads me to believe that a default setting to warn of the limit is no longer necessary. Also, some people would rather use textwidth to enforce their line lengths, rather than colorcolumn.

Furthermore, ideally the hypothetical rustfmt would save us from ever worrying about column lengths at all. Let us boldly stride towards that utopian future.