Remove extern C blocks from lib/* internal APIs (except xxhash.h)

lib/compress/zstd_fast.h

@@ -14,10 +14,6 @@
 #include "../common/mem.h"      /* U32 */
 #include "zstd_compress_internal.h"
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 void ZSTD_fillHashTable(ZSTD_matchState_t* ms,
                         void const* end, ZSTD_dictTableLoadMethod_e dtlm,
                         ZSTD_tableFillPurpose_e tfp);
@@ -31,8 +27,4 @@ size_t ZSTD_compressBlock_fast_extDict(
         ZSTD_matchState_t* ms, seqStore_t* seqStore, U32 rep[ZSTD_REP_NUM],
         void const* src, size_t srcSize);
 
-#if defined (__cplusplus)
-}
-#endif
-
 #endif /* ZSTD_FAST_H */