Fixed double delete and memory leak in RawEventFileWriterForBU

There was an obvious cut and paste error where the same variable was
used to do a delete and another variable was missed. This was fix.
In addition, there is no need to check for null before deleting a
pointer since delete does that itself.
NOTE: It would be better if these variables were converted to
std::unique_ptr<> so memory management would be automatic.
Merge pull request #3467 from Dr15Jones/fixDoubleDeleteInRawEventFileWriterForBU

Misc fix -- Fixed double delete and memory leak in RawEventFileWriterForBU