'lua_assert' moved from 'lualib.h' to 'lauxlib.h'

The macro is useful also in 'lauxlib.c', which does not include
'lualib.h'. Also, the definition was corrected to be "on" when
LUAI_ASSERT is defined.

lualib.h

@@ -49,10 +49,4 @@ LUAMOD_API int (luaopen_package) (lua_State *L);
 LUALIB_API void (luaL_openlibs) (lua_State *L);
 
 
-
-#if !defined(lua_assert)
-#define lua_assert(x)	((void)0)
-#endif
-
-
 #endif