Don't limit max line length on .u scratch files

[ceedubs]

The recently added .editorconfig sets a max line length of 120 characters for all file types. I found this to be
pretty frustrating when writing Unison scratch files. While writing Unison code my editor would seemingly randomly
create a new line, generating invalid Unison code. This came up more often when writing Doc values, since I tend to
write longer lines in prose than in code.

The formatting in scratch files is ephemeral, so I don't think that there is any good reason to force a max line length
on it.

[sellout]

This looks good.

The original settings were created primarily for Haskell, but I figured it’s good for many programming languages, so I left it with *. But we could also constrain max_line_length (and possibly other settings) to *.hs and some other explicit extensions (e.g., I like to write Markdown without line breaks … but I don’t know if that’s the style at Unison or not).

In any case, I think this change on its own is an improvement.