Remove a 6.2.x compatibility workaround
Summary: The format specifier to enable locale-aware formatting has been renamed from `n` to `L` in {fmt} and `std::format`: Now that fbcode has been updated to use the new specifier, remove the compatibility workaround.
#include "core.h"
-#ifndef FMT_DEPRECATED_N_SPECIFIER
-# define FMT_DEPRECATED_N_SPECIFIER
-#endif
-
#ifdef __INTEL_COMPILER
# define FMT_ICC_VERSION __INTEL_COMPILER
#elif defined(__ICL)
