Remove warning on explicit default config value in tests

This was added with f7a25a1, this was
to address an issue with the worthy goal[1]:

> It is probably worth auditing the tests and where they are not
deliberately testing an option, removing any options they set.

However, given the number of warnings this produces:

  $ cargo test -- --nocapture |& grep -c 'Default value.*used explicitly'
  236

I think this approach did not work, one could enforce this approach by
changing this to be an error, but I think there are valid cases to use
defaults, e.g. a reproduction of an issue relating to line length uses
the default `max_width`: it's simplest to add a test verifying the
behaviour with an explicit `max_width: 100` rather than adjusting the
reproduction.

Link: #1720 [1]

Author: matthewhughes934

src/test/mod.rs

@@ -19,7 +19,7 @@ use crate::{
 };
 
 use rustfmt_config_proc_macro::nightly_only_test;
-use tracing::{debug, warn};
+use tracing::debug;
 
 mod configuration_snippet;
 mod mod_resolver;
@@ -776,9 +776,6 @@ fn read_config(filename: &Path) -> Config {
     for (key, val) in &sig_comments {
         if key != "target" && key != "config" && key != "unstable" {
             config.override_value(key, val);
-            if config.is_default(key) {
-                warn!("Default value {} used explicitly for {}", val, key);
-            }
         }
     }