leveldb: fix cursor del for MojDbQuota

- leveldb doesn't have multi-value so doing Put is enough to overwrite
  existing entry
- m_recSize is hard to maintain so use actual information about entry
  that is going to be deleted by cursor

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <norluk@luxoft.com>
Change-Id: I9538b88d9d9282a2cec227fb28ee995212140e81