rgw/s3: remove 'aws-chunked' from Content-Encoding response

rgw/s3: remove 'aws-chunked' from Content-Encoding response

PutObject stores some of the generic http request headers in object
attrs so they can be returned as response headers in Get/HeadObject

S3 has its own `aws-chunked` value for the `Content-Encoding` header,
which it says does _not_ get stored with the object or returned with
Get/HeadObject

we've been storing this header with objects forever, so omitting the
value on PutObject doesn't fix the issue for existing objects. instead,
add the necessary filtering to Get/HeadObject

Fixes: https://tracker.ceph.com/issues/21128
Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit 4a802b864a6f9d45506197dfb1bc23cf852e51f8)