Revert quoted value zone annotation in topology injector

*Description*:
https://github.com/envoyproxy/gateway/pull/6133 double quotes the zone annotation within the topology injector. This is incorrect, as the value of `ENVOY_SERVICE_ZONE` now contains double quotes (e.g., `topology.kubernetes.io/zone: test` returns `ENVOY_SERVICE_ZONE="\"test\""`. Although there was a small discussion within the PR for this issue, my opinion is that a fix was applied for envoy-gateway when it's an issue with their cloud provider.

https://github.com/envoyproxy/gateway/pull/6133#issuecomment-2902873654