Revert version 2.1 of the IMDS credentials provider (#4187)

## Motivation and Context
We released the feature [in this
release](https://github.com/awslabs/aws-sdk-rust/releases/tag/release-2025-06-12),
but till the infrastructure is fully ready, we'll temporarily revert the
functionality.

## Testing
- CI

## Checklist
- [x] For changes to the AWS SDK, generated SDK code, or SDK runtime
crates, I have created a changelog entry Markdown file in the
`.changelog` directory, specifying "aws-sdk-rust" in the `applies_to`
key.

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._

Author: ysaito1001

.changelog/1750789932.md

@@ -0,0 +1,12 @@
+---
+applies_to:
+- aws-sdk-rust
+authors:
+- ysaito1001
+references:
+- smithy-rs#4187
+breaking: false
+new_feature: false
+bug_fix: false
+---
+Temporarily disable fetching account ID from IMDS credentials on EC2.

aws/rust-runtime/aws-config/Cargo.lock

@@ -1,6 +1,6 @@
 [package]
 name = "aws-config"
-version = "1.8.0"
+version = "1.8.1"
 authors = [
     "AWS Rust SDK Team <aws-sdk-rust@amazon.com>",
     "Russell Cohen <rcoh@amazon.com>",

aws/rust-runtime/aws-config/Cargo.toml

@@ -733,17 +733,8 @@ pub(crate) mod test {
         .unwrap()
     }
 
-    pub(crate) fn imds_response_404() -> HttpResponse {
-        HttpResponse::try_from(
-            http::Response::builder()
-                .status(404)
-                .body(SdkBody::empty())
-                .unwrap(),
-        )
-        .unwrap()
-    }
-
     pub(crate) fn make_imds_client(http_client: &StaticReplayClient) -> super::Client {
+        tokio::time::pause();
         super::Client::builder()
             .configure(
                 &ProviderConfig::no_configuration()