Revert "jclouds-565 Fixes a bug with swift where the metadata is updated, but the content-type is reset to application/x-www-form-urlencoded."

This reverts commit ac117fc3d85a02625b72e4831617e5d68d4fa376.
Issue number incorrectly specified in commit message.
JCLOUDS-565: Fixes a bug with swift where the metadata is updated, but the content-type is reset to application/x-www-form-urlencoded.

Workaround: send an empty Content-Type header, only for the updateMetadata call.
Re-commit of ac117fc with correct issue number.