Revert "TST/TEMP: fix pyqt to 4.x for plotting tests"
Reverts pydata/pandas#14240

For when https://github.com/ContinuumIO/anaconda-issues/issues/1068 is solved


I think this is partly solved on the continuum side. They have included the fix in the rc settings, but didn't bump the build number (https://github.com/ContinuumIO/anaconda-issues/issues/1068#issuecomment-255814564). So it depends on if the cached conda package is still on travis. Good question :-) (it was actually also an error that this was a branch on pandas itself)