az deployment * create samples contain incorrectly-formatted parameters

The example "Create a deployment at management group from a local template file, using parameters from a JSON string" contains incorrectly-escaped invalid JSON, and fails when run. This appears to be the same for the other equivalent examples (`az deployment sub create`, `az deployment rg create`, etc)

The example:
```bash
az deployment mg create --management-group-id testmg --name rollout01 --location WestUS \
--template-file azuredeploy.json \
--parameters '{ \"policyName\": { \"value\": \"policy2\" } }'
```

Should be:
```bash
az deployment mg create --management-group-id testmg --name rollout01 --location WestUS \
--template-file azuredeploy.json \
--parameters '{ "policyName": { "value": "policy2" } }'
```

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#### Document Details

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* ID: 9c979830-81e7-3059-ade0-4c7879cadd1c
* Version Independent ID: fc7f4352-9dae-ee17-00ea-d01ba3d12219
* Content: [az deployment mg](https://docs.microsoft.com/en-us/cli/azure/deployment/mg?view=azure-cli-latest#feedback)
* Content Source: [latest/docs-ref-autogen/deployment/mg.yml](https://github.com/MicrosoftDocs/azure-docs-cli/blob/master/latest/docs-ref-autogen/deployment/mg.yml)
* GitHub Login: @rloutlaw
* Microsoft Alias: **routlaw**