Trim trailing colons from paths to allow copy/pasting git grep -n output

[chschneider]

This is a minimalistic change to allow output from git grep -n including line numbers and a trailing colon to be copy-pasted for editing without having to remove the trailing colon, e.g.

$ git grep -n trim_end_matches
helix-term/src/args.rs:132:    let mut s = s.trim_end_matches(':').rsplitn(3, ':');
helix-term/src/args.rs:144:    let (path, row) = s.trim_end_matches(':').rsplit_once(':')?;
$ hx helix-term/src/args.rs:132:

The same change was made for git grep -n --column, i.e. the path:line:col: format.