Reduce DB access in ReceiveCommits.autoCloseChanges()

ReceiveCommits.openChangesByKey()'s local variable 'byKey' is a
Map<Change.Key, Change.Id> type, replace the Change.Id with Change
to reduce DB access.

Change-Id: Iaafebe75dfe4aecf2c0587352d394ca1e4f8de3c
1 file changed