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

lib/compress/zstd_cwksp.h

@@ -19,10 +19,6 @@
 #include "../common/portability_macros.h"
 #include "../common/compiler.h" /* ZS2_isPower2 */
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 /*-*************************************
 *  Constants
 ***************************************/
@@ -766,8 +762,4 @@ MEM_STATIC void ZSTD_cwksp_bump_oversized_duration(
     }
 }
 
-#if defined (__cplusplus)
-}
-#endif
-
 #endif /* ZSTD_CWKSP_H */