MAINT: sparse.linalg: avoid importing from `np.core`
MAINT: sparse.linalg: avoid importing from `np.core`

Currently `_norm` has the following import:

```
from numpy.core import Inf, sqrt, abs
```

this replaces it with

```
from numpy import Inf, sqrt, abs
```

since we should prefer importing from the top-level namespace.

matthew-brett/scipy,mdhaber/scipy,scipy/scipy,Stefan-Endres/scipy,person142/scipy,rgommers/scipy,WarrenWeckesser/scipy,perimosocordiae/scipy,pizzathief/scipy,ilayn/scipy,Eric89GXL/scipy,nmayorov/scipy,matthew-brett/scipy,Stefan-Endres/scipy,WarrenWeckesser/scipy,e-q/scipy,perimosocordiae/scipy,ilayn/scipy,rgommers/scipy,perimosocordiae/scipy,mdhaber/scipy,person142/scipy,rgommers/scipy,e-q/scipy,vigna/scipy,endolith/scipy,rgommers/scipy,scipy/scipy,matthew-brett/scipy,pizzathief/scipy,perimosocordiae/scipy,pizzathief/scipy,andyfaff/scipy,ilayn/scipy,WarrenWeckesser/scipy,tylerjereddy/scipy,anntzer/scipy,scipy/scipy,rgommers/scipy,ilayn/scipy,andyfaff/scipy,scipy/scipy,andyfaff/scipy,endolith/scipy,grlee77/scipy,Stefan-Endres/scipy,Eric89GXL/scipy,anntzer/scipy,zerothi/scipy,ilayn/scipy,matthew-brett/scipy,tylerjereddy/scipy,WarrenWeckesser/scipy,Eric89GXL/scipy,tylerjereddy/scipy,WarrenWeckesser/scipy,pizzathief/scipy,grlee77/scipy,endolith/scipy,person142/scipy,perimosocordiae/scipy,pizzathief/scipy,e-q/scipy,grlee77/scipy,scipy/scipy,person142/scipy,grlee77/scipy,endolith/scipy,Eric89GXL/scipy,anntzer/scipy,zerothi/scipy,tylerjereddy/scipy,anntzer/scipy,zerothi/scipy,tylerjereddy/scipy,andyfaff/scipy,grlee77/scipy,mdhaber/scipy,andyfaff/scipy,mdhaber/scipy,nmayorov/scipy,Stefan-Endres/scipy,endolith/scipy,WarrenWeckesser/scipy,scipy/scipy,vigna/scipy,e-q/scipy,mdhaber/scipy,andyfaff/scipy,mdhaber/scipy,endolith/scipy,zerothi/scipy,perimosocordiae/scipy,person142/scipy,ilayn/scipy,matthew-brett/scipy,Eric89GXL/scipy,e-q/scipy,vigna/scipy,Stefan-Endres/scipy,nmayorov/scipy,Stefan-Endres/scipy,vigna/scipy,anntzer/scipy,nmayorov/scipy,Eric89GXL/scipy,zerothi/scipy,zerothi/scipy,vigna/scipy,nmayorov/scipy,anntzer/scipy