Check the validity of the top-level Cargo.toml (#2553)

This commit updates `ci-scripts/check-aws-sdk-service` to implicitly
check whether the top-level `Cargo.toml` is valid or not. In this case,
"valid" means that examples are properly excluded from the workspace.

Co-authored-by: Yuki Saito <awsaito@amazon.com>

Author: ysaito1001

tools/ci-scripts/check-aws-sdk-services

@@ -7,9 +7,8 @@
 set -eux
 cd aws-sdk
 
-# Remove examples from workspace
-sed -i '/"examples\//d' Cargo.toml
-
+# Invoking `cargo test` at the root directory implicitly checks for the validity
+# of the top-level `Cargo.toml`
 cargo test --all-features
 
 for test_dir in tests/*; do