Remove obsolete interfaces from FastSiDigitization and FastTRT_ Digitization packages

This merge request emoves the obsolete/redundant IPixelFastDigitizationTool, ISCT_FastDigitizationTool, ISiSmearedDigitizationTool and ITRTFastDigitizationTool interfaces and additionally tidies up the PixelFastDigitization, SCT_FastDigitization, SiSmearedDigitization and TRTFastDigitization algorithms. Finally, it adds in adds a missing LINK_LIBRARY in the FastSiDigitization/CMakeLists.txt file. (During this clean-up it was noted in the FastTRT_ Digitization/CMakeLists.txt file that this package has a dependency on a package which only builds a component library. This will be cleaned-up in a separate merge request.)