remove Python2 compatibility: no more imports from the future

wetb/__init__.py

wetb/control/control.py

wetb/control/tests/test_control.py

wetb/dlc/high_level.py

wetb/dlc/tests/test_high_level.py

wetb/fast/fast_io.py

wetb/fast/tests/test_fast_io.py

wetb/fatigue_tools/bearing_damage.py

wetb/fatigue_tools/fatigue.py

wetb/fatigue_tools/rainflowcounting/pair_range.py

wetb/fatigue_tools/rainflowcounting/peak_trough.py

wetb/fatigue_tools/rainflowcounting/rainflowcount.py

wetb/fatigue_tools/rainflowcounting/rainflowcount_astm.py

wetb/fatigue_tools/tests/test_bearing_damage.py

wetb/fatigue_tools/tests/test_fatigue.py

wetb/gtsdf/__init__.py

wetb/gtsdf/gtsdf.py

wetb/gtsdf/tests/test_gtsdf.py

wetb/gtsdf/tests/test_gtsdf_stat.py

wetb/gtsdf/tests/test_unix_time.py