Remove duplicate content type header in assign blob holder request to blob service.
In testing my farcaster bot, calls to createOrUpdatePublicLink were failing as it would eventually call assignBlobHolder with two duplicate content-type headers, resulting in a 400 Bad Request from the blob service.
We can fix this by specifying createRequestHeaders's includeContentType parameter as false
Linear Issue: https://linear.app/comm/issue/ENG-9986/running-into-an-issue-of-createorupdatepubliclink-failing-to-upload-a