The only two ways I know would be...
Option 1: Right click on the midi clip at bar 6 and select split clip. When the clip splits, it will either be hi-lited to the left (which would be bars 1-6) or to the right. Make sure the left part of the split is hi-lited and press the delete key.
Opion 2: Double click on the midi file to bring up piano roll view. Left click and hold while dragging to lasso bars 1-6, release left click...press the delete key.
Hope this is what you were after.
-Danny