In logging format, use PRIu64 instead of casting

Summary: Code cleaning up, since we are already using __STDC_FORMAT_MACROS in printing uint64_t, change other places. Only logging is changed.

Test Plan: make all check

Reviewers: ljin

Reviewed By: ljin

Subscribers: dhruba, yhchiang, haobo, leveldb

Differential Revision: https://reviews.facebook.net/D19113