message: Correct add_weight docstring by removing mention of outdated functionality.
diff: @@ -256,7 +256,7 @@ class Layer(checkpointable.Checkpointable):
  synchronization=tf_variables.VariableSynchronization.AUTO,
  aggregation=tf_variables.VariableAggregation.NONE,
  **kwargs):
  - """Adds a new variable to the layer, or gets an existing one; returns it.
  + """Adds a new variable to the layer.
  Arguments:
  name: variable name.
  