Remove grid icons deprecation warning (nushell#14526)

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# Description
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Noticed this TODO, so I did as it said.

# User-Facing Changes
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N/A (the functionality was already removed)

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---------

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

crates/nu-protocol/src/config/error.rs

@@ -65,6 +65,8 @@ impl<'a> ConfigErrors<'a> {
         });
     }
 
+    // We'll probably need this again in the future so allow dead code for now
+    #[allow(dead_code)]
     pub fn deprecated_option(&mut self, path: &ConfigPath, suggestion: &'static str, span: Span) {
         self.error(ConfigError::Deprecated {
             path: path.to_string(),

crates/nu-protocol/src/config/mod.rs

@@ -156,10 +156,6 @@ impl UpdateFromValue for Config {
                 "filesize" => self.filesize.update(val, path, errors),
                 "explore" => self.explore.update(val, path, errors),
                 "color_config" => self.color_config.update(val, path, errors),
-                "use_grid_icons" => {
-                    // TODO: delete it after 0.99
-                    errors.deprecated_option(path, "use `grid -i`", val.span());
-                }
                 "footer_mode" => self.footer_mode.update(val, path, errors),
                 "float_precision" => self.float_precision.update(val, path, errors),
                 "use_ansi_coloring" => self.use_ansi_coloring.update(val, path, errors),