fix(rust,client): re-enable TLS support for reqwest with supportAsync

[PiDelport]

The existing reqwest codegen disables the default reqwest crate features when supportAsync=true: this inadvertently has the effect of disabling reqwest's TLS support entirely.

This PR keeps the default features, which matches the behaviour of supportAsync=false, and keeps the default TLS support enabled.

• Tracking issue: [BUG][RUST] Twilio OpenAPI codegen errors #10421

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[wing328]

Rust petstore tests passed via https://app.travis-ci.com/github/OpenAPITools/openapi-generator/builds/238202751

[wing328]

LGMT. Thanks for the enhancement.