MAINT: _lib/ccallback: remove unused code
MAINT: _lib/ccallback: remove unused code

LowLevelCallable never contains a Python callable, so no need to check
for it in the C code.

gfyoung/scipy,mdhaber/scipy,WarrenWeckesser/scipy,jamestwebber/scipy,tylerjereddy/scipy,ilayn/scipy,Eric89GXL/scipy,jamestwebber/scipy,zerothi/scipy,andyfaff/scipy,Eric89GXL/scipy,aarchiba/scipy,rgommers/scipy,tylerjereddy/scipy,WarrenWeckesser/scipy,Eric89GXL/scipy,aarchiba/scipy,jamestwebber/scipy,matthew-brett/scipy,tylerjereddy/scipy,endolith/scipy,e-q/scipy,gfyoung/scipy,anntzer/scipy,gfyoung/scipy,scipy/scipy,rgommers/scipy,ilayn/scipy,vigna/scipy,zerothi/scipy,mdhaber/scipy,endolith/scipy,jor-/scipy,e-q/scipy,arokem/scipy,grlee77/scipy,aarchiba/scipy,arokem/scipy,matthew-brett/scipy,scipy/scipy,tylerjereddy/scipy,gertingold/scipy,vigna/scipy,aeklant/scipy,scipy/scipy,gertingold/scipy,Stefan-Endres/scipy,nmayorov/scipy,lhilt/scipy,endolith/scipy,perimosocordiae/scipy,grlee77/scipy,perimosocordiae/scipy,ilayn/scipy,Stefan-Endres/scipy,lhilt/scipy,mdhaber/scipy,person142/scipy,gfyoung/scipy,mdhaber/scipy,gertingold/scipy,anntzer/scipy,tylerjereddy/scipy,zerothi/scipy,perimosocordiae/scipy,anntzer/scipy,pizzathief/scipy,pizzathief/scipy,WarrenWeckesser/scipy,jamestwebber/scipy,pizzathief/scipy,perimosocordiae/scipy,aarchiba/scipy,scipy/scipy,gfyoung/scipy,ilayn/scipy,aeklant/scipy,Eric89GXL/scipy,jor-/scipy,gertingold/scipy,jor-/scipy,grlee77/scipy,grlee77/scipy,person142/scipy,anntzer/scipy,Stefan-Endres/scipy,lhilt/scipy,mdhaber/scipy,lhilt/scipy,WarrenWeckesser/scipy,zerothi/scipy,person142/scipy,e-q/scipy,WarrenWeckesser/scipy,arokem/scipy,vigna/scipy,Stefan-Endres/scipy,arokem/scipy,person142/scipy,pizzathief/scipy,anntzer/scipy,ilayn/scipy,Stefan-Endres/scipy,aeklant/scipy,lhilt/scipy,zerothi/scipy,nmayorov/scipy,rgommers/scipy,e-q/scipy,grlee77/scipy,mdhaber/scipy,endolith/scipy,jor-/scipy,endolith/scipy,anntzer/scipy,aeklant/scipy,gertingold/scipy,aeklant/scipy,pizzathief/scipy,ilayn/scipy,Eric89GXL/scipy,vigna/scipy,perimosocordiae/scipy,aarchiba/scipy,andyfaff/scipy,nmayorov/scipy,rgommers/scipy,matthew-brett/scipy,person142/scipy,andyfaff/scipy,arokem/scipy,WarrenWeckesser/scipy,jamestwebber/scipy,zerothi/scipy,andyfaff/scipy,andyfaff/scipy,endolith/scipy,scipy/scipy,matthew-brett/scipy,nmayorov/scipy,rgommers/scipy,nmayorov/scipy,matthew-brett/scipy,e-q/scipy,perimosocordiae/scipy,scipy/scipy,Stefan-Endres/scipy,Eric89GXL/scipy,andyfaff/scipy,jor-/scipy,vigna/scipy