Compaction Filter V1 to use old context struct to keep backward compatible

Summary: The previous change D15087 changed existing compaction filter, which makes the commonly used class not backward compatible. Revert the older interface. Use a new interface for V2 instead.

Test Plan: make all check

Reviewers: haobo, yhchiang, igor

CC: danguo, dhruba, ljin, igor, leveldb

Differential Revision: https://reviews.facebook.net/D17223