Pinned botocore / boto3 conflict

There is a conflict in the versions specified in `requirements.txt`

https://github.com/aws/codeartifact-origin-control-toolkit/blob/9a6c23e11e769ee285f39849e110af24aa281d15/requirements.txt#L1-L2

```
ERROR: Cannot install -r requirements.txt (line 1) and botocore==1.27.8 because these package versions have conflicting dependencies.

The conflict is caused by:
The user requested botocore==1.27.8
boto3 1.24.30 depends on botocore<1.28.0 and >=1.27.30
```

As `boto3` internally specifies a `botocore` version the problem appears to be resolved by commenting `botocore`.