Do not set Content-MD5 in S3.

[teo-tsirpanis]

SC-52300

This PR removes setting the Content-MD5 header on S3 uploads. There are multiple reasons for this:

• The header is not supported on directory buckets used by S3 Express One Zone.
• Computing the MD5 hash of the data immediately before uploading them has a performance overhead and does not provide additional security.
• We don't do a similar thing in the other cloud VFSes.

Validated by:

• Creating, writing, consolidating and vacuuming an array on a directory bucket.
• Running quickstart_dense_cpp on a Google Cloud Storage bucket using the S3 compatibility API.

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TYPE: BUG
DESC: Fix incompatibilities with S3 Express One Zone, by stopping setting Content-MD5 on all S3 uploads.