DOC: Fix the documented signatures of four `ufunc` methods (#17199)
DOC: Fix the documented signatures of four `ufunc` methods (#17199)

* DOC: Clarify that a number of ufunc-related parameters are positional-only

* DOC: Fixed an incorrect parameter name

`a' should be `array` in `np.ufunc.reduce()`

* DOC: Fixed an incorrect parameter name in `ufunc.reduceat`

* DOC: Replace all leftover references to `a` with `array`

* DOC: Replace two more leftover references to `a` with `array`
pdebuyl/numpy,jakirkham/numpy,simongibbons/numpy,endolith/numpy,grlee77/numpy,mhvk/numpy,grlee77/numpy,endolith/numpy,mhvk/numpy,pbrod/numpy,jakirkham/numpy,pdebuyl/numpy,grlee77/numpy,numpy/numpy,simongibbons/numpy,mhvk/numpy,mattip/numpy,grlee77/numpy,madphysicist/numpy,simongibbons/numpy,madphysicist/numpy,numpy/numpy,madphysicist/numpy,pdebuyl/numpy,simongibbons/numpy,mattip/numpy,jakirkham/numpy,pbrod/numpy,pbrod/numpy,anntzer/numpy,numpy/numpy,jakirkham/numpy,grlee77/numpy,pbrod/numpy,anntzer/numpy,charris/numpy,madphysicist/numpy,endolith/numpy,numpy/numpy,simongibbons/numpy,rgommers/numpy,madphysicist/numpy,mhvk/numpy,rgommers/numpy,rgommers/numpy,mhvk/numpy,jakirkham/numpy,pdebuyl/numpy,mattip/numpy,charris/numpy,rgommers/numpy,mattip/numpy,seberg/numpy,seberg/numpy,pbrod/numpy,charris/numpy,seberg/numpy,charris/numpy,endolith/numpy,anntzer/numpy,anntzer/numpy,seberg/numpy