RAVEN query only deleting half of values

https://git.ligo.org/lscsoft/raven/blob/master/ligo/raven/search.py#L100

Since we are removing values inside of for loops we end up skipping over every other value (this for loop activated when group is not None). This led to superevents being found within Burst window when their preferred events were CBCs.

An example of this error is in playground with external event: https://gracedb-playground.ligo.org/events/E18996/view/ Note that there were two superevents within the Burst Raven window and the second was found in coincidence

This occurred again with external event https://gracedb-playground.ligo.org/events/E19252/view/ where three superevents were in the window (again second chosen)