MAINT: clean-up imports in _dwt.pyx
MAINT: clean-up imports in _dwt.pyx

Some imports are no longer necessary after previous refactoring. Remove
them.

eriol/pywt,rgommers/pywt,rgommers/pywt,PyWavelets/pywt,eriol/pywt,grlee77/pywt,rgommers/pywt,PyWavelets/pywt,kwohlfahrt/pywt,grlee77/pywt,kwohlfahrt/pywt,rgommers/pywt,kwohlfahrt/pywt,eriol/pywt,michelp/pywt,michelp/pywt,michelp/pywt