Remove broken line from transpiler passes tutorial

The transpiler passes tutorial was previously replacing the 'properties'
attribute of the FakeTokyo backend with an empty dictionary {}. However,
this is a type violation as properties is defined (and has been for a
very long time) as a method in the base abstract backend class. [1] This
didn't block anything because nothing the call path of the notebook was
using properties as a callable before. But in terra 0.15.0 this has
changed and backend.properties() is accessed in the setup for a
transpilation and this is causing a failure. This commit removes the use
overloading of the attribute as it doesn't seem to serve a purpose
anymore (I presume it was there for when NoiseAdaptiveLayout was in
level 3) which will unblock Qiskit/qiskit#998

[1] https://github.com/Qiskit/qiskit-terra/blob/master/qiskit/providers/basebackend.py#L65

Author: mtreinish