chore: remove breaking changes comment from PR template (#29036)

### Issue # (if applicable)

n/a

### Reason for this change

If the comment is accidentally left in the PR description the PR could get incorrectly flagged for having breaking changes

### Description of changes

Remove breaking changes comment from PR description

### Description of how you validated changes


### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: gracelu0

.github/PULL_REQUEST_TEMPLATE.md

@@ -17,14 +17,6 @@ Closes #<issue number here>.
 ### Checklist
 - [ ] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)
 
-<!--Does this PR includes breaking changes? If it does, list them here in the following format (notice how multiple breaking changes should be formatted):
-
-  ```
-  BREAKING CHANGE: Description of the breaking change, the previous behaviour, and the new behaviour. 
-  * **module-name:** Another breaking change
-  * **module-name:** Yet another breaking change
-  ```
--->
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 *By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*