Summary:
This was previously broken, as the performance context-related
macro signatures in file monitoring/perf_context_imp.h
deviated for the case when NPERF_CONTEXT was defined and when it
was not.

Update the macros for the `-DNPERF_CONTEXT` case, so it compiles.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5704

Differential Revision: D16867746

fbshipit-source-id: 05539724cb1f7955ecc42828365836a677759ad9