make the blob params in the event stream tests not b64

[lucix-aws]

Background

• What do these changes do?
  • All of the blob params in our protocoltests are plaintext, but some in the new eventstream ones were b64
• Why are they important?
  • consistency

Testing

• How did you test these changes?
  • Ran the event stream tests in smithy-go

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[github-actions]

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