Fix compilation of Python Bindings on Windows

[traversaro]

Without this fix, the compilation of Python bindings is failing with error:

2021-03-22T08:34:49.9037393Z   -- Found Python3: C:/Miniconda/envs/test/python.exe (found version "3.9.2") found components: Interpreter Development Development.Module Development.Embed 
2021-03-22T08:34:49.9045986Z   CMake Error at bindings/python/CMakeLists.txt:17 (get_filename_component):
2021-03-22T08:34:49.9047185Z     get_filename_component called with incorrect number of arguments
2021-03-22T08:34:49.9047925Z   
2021-03-22T08:34:49.9079080Z   -- Configuring incomplete, errors occurred!

The reason is that for the modern FindPython3 CMake module Python3_LIBRARY is not an output, so the code does not work. However, the whole logic seems not to be necessary anymore with modern CMake and modern Python (tested with Python 3.9), so I think we can just remove it altogether.

[sonarqubecloud]

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[drdanz]

Merged, thanks.