CI: remove codecov from CircleCI and clean up runtests command
CI: remove codecov from CircleCI and clean up runtests command

Nothing changed in the runtests.py invocation, it's just more
readable now.

codecov wasn't used, and the recent security incident shows it's
better not to mix it with CI jobs that require tokens or SSH keys
for deployment.

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