Simplify build-system removing unused CMake macros & variables related to i18n

[jcfr]

Is your feature request related to a problem? Please describe.

Following the introduction of the Translation update helper script through #6674, the processing of the sources can be done directly without having to rely on CMake.

Describe the solution you'd like

To streamline the overall maintenance of the build-system, the proposed updates are:

• Remove SlicerMacroTranslation.cmake and update module using it:
  • SlicerMacroBuildModuleWidgets.cmake
  • SlicerMacroBuildApplication.cmake
  • SlicerMacroBuildBaseQtLibrary.cmake
  • SlicerMacroBuildLoadableModule.cmake
• Remove global property Slicer_QM_OUTPUT_DIRS
• Remove support for QM_OUTPUT_FILES
• Confirm that the use of Slicer_QM_DIR and Slicer_QM_OUTPUT_DIRS in vtkSlicerConfigure.h.in and SlicerDirectories.cmake is still relevant.

Describe alternatives you've considered

Move forward with improving CMake support initiated in these pull-requests:

• I18n add targets for generating qm files and translation templates #6125
• Improve i18n support #6050

Additional context

NA