MAINT: Remove filter copy in upsampling_convolution_valid_sf
MAINT: Remove filter copy in upsampling_convolution_valid_sf

No need to copy the filter, in fact profiling suggests a slight speed increase
if the copy is removed.

NOTE: Removing the intermediate sum_x variables, and adding directly to the
output increases floating point error (3.27e-7 rather than < 3e-7).

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