MAINT: remove unused file c_string.pxd.
MAINT: remove unused file c_string.pxd.

PyWavelets/pywt,kwohlfahrt/pywt,PyWavelets/pywt,eriol/pywt,rgommers/pywt,rgommers/pywt,rgommers/pywt,kwohlfahrt/pywt,ThomasA/pywt,michelp/pywt,ThomasA/pywt,eriol/pywt,kwohlfahrt/pywt,rgommers/pywt,Dapid/pywt,Dapid/pywt,aaren/pywt,Dapid/pywt,eriol/pywt,ThomasA/pywt,grlee77/pywt,grlee77/pywt,michelp/pywt,michelp/pywt,aaren/pywt,aaren/pywt