Fix compiling S3 crate for wasm (#3590)

## Motivation and Context
Running `cargo build --target wasm32-unknown-unknown
--no-default-features` on an S3 crate has stopped working since
https://github.com/smithy-lang/smithy-rs/pull/3465 with the following
error:
```
error: the wasm*-unknown-unknown targets are not supported by default, you may need to enable the "js" feature. For more information see: https://docs.rs/getrandom/#webassembly-support
   --> /Users/[REDACTED]/.cargo/registry/src/index.crates.io-6f17d22bba15001f/getrandom-0.2.14/src/lib.rs:352:9
    |
352 | /         compile_error!("the wasm*-unknown-unknown targets are not supported by \
353 | |                         default, you may need to enable the \"js\" feature. \
354 | |                         For more information see: \
355 | |                         https://docs.rs/getrandom/#webassembly-support");
    | |________________________________________________________________________^
```

To address the issue, this PR updates an S3's dependency on `ahash` in a
way that disables default features.

## Testing
Updated the existing test `integration-tests/webassembly` so that
`check-aws-sdk-standalone-integration-tests` will run `cargo check`
`aws-sdk-s3` against both `wasm32-wasi` and `wasm32-unknown-unknown`
(the updated check would break if we removed `default-features = false`
from the `ahash` dependency).

## Checklist
- [x] I have updated `CHANGELOG.next.toml` if I made changes to the AWS
SDK, generated SDK code, or SDK runtime crates

----

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