[dnn] add various linear layers (#407)

[dnn] add various linear layers

Author: ztqakita

brainpy/__init__.py

@@ -64,7 +64,6 @@
   dyn,  # dynamics module
   # delay,  # delay module
 )
-from brainpy._src.delay import (DataDelay, TargetDelay)
 
 from brainpy.synapses import (
   synouts,  # synaptic output

brainpy/_src/connect/random_conn.py

@@ -863,7 +863,7 @@ class PowerLaw(TwoEndConnector):
          Phys. Rev. E, 65, 026107, 2002.
   """
 
-  def __init__(self, m, p, directed=False, seed=None, **kwargs):
+  def __init__(self, m: int, p: float, directed=False, seed=None, **kwargs):
     super(PowerLaw, self).__init__(**kwargs)
     self.m = m
     self.p = p