MITK can be configured with the option -DMITK_USE_Qt5:BOOL=OFF. The result should be that MITK does not need Qt5 and all related projects are not built.
However, building with that option gives me the following error:
CMake Error at GUISupport/Qt/CMakeLists.txt: 72 [...] Could not find a package configuration file provided by "Qt5" with any of the following names: [...]
CMake Error at CMake/ctkmactroSetupQt.cmake: 50 [...] Could not find a package configuration file provided by "Qt5" with any of the following names: [...]