Examples: Remove unneeded setting of CMP0020 policy to NEW

Since CMake 3.3 is required, the policy is implicitly set.

See https://cmake.org/cmake/help/v3.3/manual/cmake-policies.7.html
and https://cmake.org/cmake/help/v3.3/manual/cmake-policies.7.html#introduction

Examples/Build/vtkMy/CMakeLists.txt

 cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
-if(POLICY CMP0020)
-  cmake_policy(SET CMP0020 NEW)
-endif()
-
 
 #
 # Set the project name.

Examples/CMakeLists.txt

 cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
-if(POLICY CMP0020)
-  cmake_policy(SET CMP0020 NEW)
-endif()
-
 
 PROJECT(VTKExamples)
 include_regular_expression("^.*$")

Examples/Infovis/Cxx/CMakeLists.txt

 cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
-if(POLICY CMP0020)
-  cmake_policy(SET CMP0020 NEW)
-endif()
 
 project(Infovis)