BUG: Fix reference count leak
BUG: Fix reference count leak

This adds a missing decref to the signature/dtype keyword argument
logic in reductions.
(The code will change quite a bit after 1.21, but this avoids a
reference count leak on 1.21.)

endolith/numpy,pdebuyl/numpy,charris/numpy,jakirkham/numpy,mattip/numpy,anntzer/numpy,charris/numpy,simongibbons/numpy,charris/numpy,simongibbons/numpy,mhvk/numpy,jakirkham/numpy,jakirkham/numpy,mhvk/numpy,jakirkham/numpy,mhvk/numpy,mhvk/numpy,rgommers/numpy,mattip/numpy,mattip/numpy,anntzer/numpy,numpy/numpy,charris/numpy,jakirkham/numpy,mattip/numpy,anntzer/numpy,seberg/numpy,rgommers/numpy,anntzer/numpy,seberg/numpy,numpy/numpy,mhvk/numpy,endolith/numpy,simongibbons/numpy,rgommers/numpy,seberg/numpy,simongibbons/numpy,endolith/numpy,pdebuyl/numpy,pdebuyl/numpy,simongibbons/numpy,rgommers/numpy,seberg/numpy,numpy/numpy,numpy/numpy,endolith/numpy,pdebuyl/numpy