Remove CMake policy guard around protobuf

Author: DownerCase

thirdparty/protobuf/build-protobuf.cmake

@@ -30,10 +30,7 @@ if(MSVC)
 endif()
 
 ecal_disable_all_warnings()
-ecal_variable_push(CMAKE_POLICY_VERSION_MINIMUM)
-set(CMAKE_POLICY_VERSION_MINIMUM 3.5)
 add_subdirectory("${CMAKE_CURRENT_LIST_DIR}/protobuf" "${eCAL_BINARY_DIR}/thirdparty/protobuf" SYSTEM)
-ecal_variable_pop(CMAKE_POLICY_VERSION_MINIMUM)
 ecal_restore_warning_level()
 
 if (NOT TARGET protobuf::libprotobuf)