gitignore: remove FIXME comment about passing path

I looked through the code for the `ignore` crate, and this optional path
is not used anywhere. The only reason to pass it would be to be able to
get the path from the `Glob` when we call `Gitignore::matched` or
`Gitignore::matched_path_or_any_parents`, but we ignore the returned
`Glob` completely anyway. Passing the path would require an unnecessary
clone of the path for each line in every .gitignore file, so it's better
not to pass it since we don't need it.

lib/src/gitignore.rs

@@ -76,8 +76,9 @@ impl GitIgnoreFile {
                     line: String::from_utf8_lossy(input_line).to_string(),
                     source: err,
                 })?;
-            // FIXME: do we need to provide the `from` argument? Is it for providing
-            // diagnostics or correctness?
+            // The `from` argument doesn't provide any diagnostics or correctness, so it is
+            // not required. It only allows retrieving the path from the `Glob` later, which
+            // we never do.
             builder
                 .add_line(None, line)
                 .map_err(|err| GitIgnoreError::Underlying {