[Workers] Remove experimental flag in waku framework guide

[rmarscher]

Summary

The --experimental flag is not needed for create-cloudflare --framework waku. It was removed in the final merged version of cloudflare/workers-sdk#8314 and we missed updating these docs. When used, it results in an error:

Error: Unsupported framework: waku

Documentation checklist

• The documentation style guide has been adhered to.

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