`--statement-typename-introspection=false` Flag Fails to Remove `__typename` in Generated Types

### Environment information

```plain text
System:
OS: Windows 10 10.0.19045
CPU: (8) x64 Intel(R) Core(TM) i7-4770K CPU @ 3.50GHz
Memory: 14.02 GB / 31.95 GB
Binaries:
Node: 20.11.1 - F:\Program Files\nodejs\node.EXE
Yarn: undefined - undefined
npm: 10.2.4 - F:\Program Files\nodejs\npm.CMD
pnpm: undefined - undefined
NPM Packages:
@aws-amplify/auth-construct: 1.5.1
@aws-amplify/backend: 1.11.0
@aws-amplify/backend-auth: 1.4.2
@aws-amplify/backend-cli: 1.4.5
@aws-amplify/backend-data: 1.3.0
@aws-amplify/backend-deployer: 1.1.12
@aws-amplify/backend-function: 1.10.0
@aws-amplify/backend-output-schemas: 1.4.0
@aws-amplify/backend-output-storage: 1.1.4
@aws-amplify/backend-secret: 1.1.5
@aws-amplify/backend-storage: 1.2.4
@aws-amplify/cli-core: 1.2.1
@aws-amplify/client-config: 1.5.4
@aws-amplify/deployed-backend-client: 1.5.0
@aws-amplify/form-generator: 1.0.3
@aws-amplify/model-generator: 1.0.11
@aws-amplify/platform-core: 1.4.0
@aws-amplify/plugin-types: 1.6.0
@aws-amplify/sandbox: 1.2.8
@aws-amplify/schema-generator: 1.2.6
aws-amplify: 6.10.2
aws-cdk: 2.173.4
aws-cdk-lib: 2.172.0
typescript: 5.7.2
No AWS environment variables
No CDK environment variables
```

### Describe the bug

When running the following command:
```bash
npx ampx generate graphql-client-code \
--out ./src/store/api/generated \
--format graphql-codegen \
--statement-typename-introspection=false
```
the generated TypeScript types *still* contain `__typename` fields, even though `--statement-typename-introspection=false` is supposed to prevent them. Meanwhile, the actual `client.models.*` responses from Amplify do **not** include these `__typename` properties, leading to mismatched shapes in the generated types vs. the returned data.

### Reproduction steps

1. **Install** or **update** Amplify / ampx:
```bash
npm install -g ampx
```
2. **Run** the codegen command in your project:
```bash
npx ampx generate graphql-client-code \
--out ./src/store/api/generated \
--format graphql-codegen \
--statement-typename-introspection=false
```
3. **Observe** that the generated files in `./src/store/api/generated` still include `__typename` fields.
4. **Compare** the returned objects from `client.models.*` (which do not include `__typename`) to the generated types (which do include it) and note the mismatch.