Revert 'hides table header while users load.'

This reverts commit 0dc12a3737127aad28be12f9417d2a63601a88ff.

Reverts https://github.com/owncloud/core/pull/9330 because it caused https://github.com/owncloud/core/issues/9368

https://github.com/owncloud/core/issues/8873 needs to be reopened after merging.

@jancborchardt @raghunayyar @MorrisJobke