Remove unneeded div-wrapper of Sync.ListComponent

_renderMainAsSelect wrapped the select field with a div, contrary to the
comment of the _div attribute. On renderUpdate calls, this div remained in
the DOM causing an increasingly deep hierarchy of div wrappers around
the select element. This fix removes the div.
Merge branch 'hotfix/superfluous-selectfield-divs' of github.com:exxcellent/echo3 into exxcellent