memHierarchy: MemEvent handling for dropped prefetch requests

[tchandrahas]

I observed that when the prefetcher(cachelistener) is enabled for MESI inclusive coherency protocol. Memory footprints keeps increasing with the simulation time. Memory footprint increasing as a result of the live events. I reverse engineered the number of live event to be similar to that of the dropped prefetch requests for my simulation. It seems to be that the (MemEvent*) event handlers for prefetch requests that are cache miss, but are unable to be allocated a MSHR position due to droplevel or outstandingPrefetches is not deleted.
Check handleGetS() -> switch(state) -> case I Nothing is done to the MemEvent when the status is Reject.

If the deletion is handled else where, let me know.

Steps to Reproduce
MESI Inclusive with any prefetcher