Revert commit 462a06ea as it causes many regressions. Use KIO::synchronousRun

to fulfill synchrounous XmlHttpRequest instead.

Unofrtunately this means that the fix for the crash reported in bug# 287778
is reverted until we can find a solution for the side effects of using nested
event loops.

BUG: 297954
BUG: 299590
CCBUG: 299710
CCBUG: 287778
FIXED-IN: 4.8.4