breaking: Remove make test-util and optional feature (#608)

* breaking: Remove make test-util and optional feature

for historical reasons, `test-util` was enabled by default in aws-hyper. This change:
* removes the pub use for test util in aws-hyper
* updates usages to use it in smithy-client
* updates the crate dependencies to correctly pull in the new feature but only for development

NOTE: please wait for a full cargoTest all crates prior to merging this change.

* Update CHANGELOG.md

* fix non-optional smithy client dependencies

* Update CHANGELOG.md

Co-authored-by: John DiSanti <jdisanti@amazon.com>

Co-authored-by: John DiSanti <jdisanti@amazon.com>