apply suggestions from code review.

Author: jverswijver

datajoint/blob.py

@@ -163,7 +163,6 @@ def read_blob(self, n_bytes=None):
                 "F": self.read_recarray,  # numpy array with fields, including recarrays
                 "d": self.read_decimal,  # a decimal
                 "t": self.read_datetime,  # date, time, or datetime
-                "T": self.read_int64_datetime,  # np.datetime64
                 "u": self.read_uuid,  # UUID
             }[data_structure_code]
         except KeyError:
@@ -199,15 +198,13 @@ def pack_blob(self, obj):
                 return self.pack_float(obj)
         if isinstance(obj, np.ndarray) and obj.dtype.fields:
             return self.pack_recarray(np.array(obj))
-        if isinstance(obj, np.number):
+        if isinstance(obj, (np.number, np.datetime64)):
             return self.pack_array(np.array(obj))
         if isinstance(obj, (bool, np.bool_)):
             return self.pack_array(np.array(obj))
         if isinstance(obj, (float, int, complex)):
             return self.pack_array(np.array(obj))
-        if isinstance(
-            obj, (datetime.datetime, datetime.date, datetime.time, np.datetime64)
-        ):
+        if isinstance(obj, (datetime.datetime, datetime.date, datetime.time)):
             return self.pack_datetime(obj)
         if isinstance(obj, Decimal):
             return self.pack_decimal(obj)
@@ -538,18 +535,12 @@ def read_datetime(self):
         )
         return time and date and datetime.datetime.combine(date, time) or time or date
 
-    def read_int64_datetime(self):
-        data = self.read_value()
-        return data.astype("datetime64[us]")
-
     @staticmethod
     def pack_datetime(d):
         if isinstance(d, datetime.datetime):
             date, time = d.date(), d.time()
         elif isinstance(d, datetime.date):
             date, time = d, None
-        elif isinstance(d, np.datetime64):
-            return b"T" + (d.astype("datetime64[us]")).tobytes()
         else:
             date, time = None, d
         return b"t" + (