Remove grid icons deprecation warning (#14526)

<!--
if this PR closes one or more issues, you can automatically link the PR
with
them by using one of the [*linking
keywords*](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword),
e.g.
- this PR should close #xxxx
- fixes #xxxx

you can also mention related issues, PRs or discussions!
-->

# Description
<!--
Thank you for improving Nushell. Please, check our [contributing
guide](../CONTRIBUTING.md) and talk to the core team before making major
changes.

Description of your pull request goes here. **Provide examples and/or
screenshots** if your changes affect the user experience.
-->

Noticed this TODO, so I did as it said.

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->
N/A (the functionality was already removed)

# Tests + Formatting
<!--
Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use toolkit.nu; toolkit test stdlib"` to run the
tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->
N/A

# After Submitting
<!-- If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
-->
N/A

---------

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),