webadmin: DialogBoxWithKeyHandlers - remove ONKEYPRESS event

DialogBoxWithKeyHandlers -> onPreviewNativeEvent:
remove ONKEYPRESS event as onKeyPress might be called
twice (due to ONKEYDOWN event). Which causes double
execution of OK command when pressing enter key
in Network dialog.

Change-Id: If63ae06dfed4956ca672c32045dbdaa16301cd45
Bug-Url: https://bugzilla.redhat.com/1058652
Signed-off-by: Daniel Erez <derez@redhat.com>