This reverts commit 2bee6f5b.

This expression is not used, and has a semantic which is not completely
optimal (namely considering utility targets to be targets, though
usually we are interested in linkable targets).

Remove it so that we have more freedom to define better expressions in
the future.

Conflicts:
        Source/cmGeneratorExpressionEvaluator.cxx
        Tests/CMakeCommands/target_compile_definitions/CMakeLists.txt
        Tests/CMakeCommands/target_compile_definitions/consumer.cpp