[ZODB-Dev] Proposing to drop some DB decoys

[Tim Peters]

[Tim Peters]
>> The database (ZODB.DB.DB) class contains 3 related public methods I'd
>> like to get rid of for ZODB 3.3:
>>
>>     cacheMeanAge()
>>     cacheMeanDeac()
>>     cacheMeanDeal()

Nobody objected, and several +1'ed, so they're gone.  Also removed
cacheStatistics(), which was also undocumented, untested, unused, and which
always returned an empty tuple.