cython: change shared_ptr invocation to libcpp.memory

python/opendht_cpp.pxd

@@ -20,17 +20,11 @@ from libcpp cimport bool
 from libcpp.string cimport string
 from libcpp.vector cimport vector
 from libcpp.utility cimport pair
+from libcpp.memory cimport shared_ptr
 
 ctypedef uint16_t in_port_t
 ctypedef unsigned short int sa_family_t;
 
-cdef extern from "<memory>" namespace "std" nogil:
-    cdef cppclass shared_ptr[T]:
-        shared_ptr() except +
-        T* get()
-        T operator*()
-        void reset(T*)
-
 cdef extern from "<functional>" namespace "std" nogil:
     cdef cppclass hash[T]:
         hash() except +