Trim Hlint diagnostic messages

[emlautarom1]

Hlint diagnostic messages contain the full path of the current file and row:column of the suggestion, with a "Suggestion" prefix. This makes the diagnostic verbose with no real benefit.

This may not affect most users, but since I'm currently using Error Lens, the result is pretty annoying. See the following example comparing type-check errors and hlint suggestions:

[ndmitchell]

I think writing our own Idea to string conversion would make sense. CC @jneira

[emlautarom1]

I see that there's been some discussion about this issue in the hls repo: haskell/haskell-language-server#553

[jneira]

@emlautarom1 the issue was fixed in master by haskell/haskell-language-server#598
could you try that version?

[emlautarom1]

@jneira Indeed, the issue was fixed. This is the current output:

Some context:

• Commit ecafd3efe9e4fc73f6275db4cfa78e0ea8936106 (output from git log -1 --format="%H").
• Built with GHC 8.8.4, cabal-install 3.2.0.0 on Fedora 33