Fix cleanup of empty pool keys in connector
Fix cleanup of empty pool keys in connector

Issues #253 and #254 implemented a `_conns` key evince logic in the
function that actually **adds** items to `_conns`

Issue #406 tweaked this logic even more, making early and eviction
of reusable items in the pool possible.

Here we put the key eviction logic where it belongs: in the method
that **removes** items from the `_conns` pool.

elastic-coders/aiohttp,vasylbo/aiohttp,singulared/aiohttp,moden-py/aiohttp,z2v/aiohttp,arthurdarcet/aiohttp,rutsky/aiohttp,jettify/aiohttp,KeepSafe/aiohttp,KeepSafe/aiohttp,avanov/aiohttp,rutsky/aiohttp,vaskalas/aiohttp,moden-py/aiohttp,panda73111/aiohttp,panda73111/aiohttp,flying-sheep/aiohttp,hellysmile/aiohttp,jettify/aiohttp,juliatem/aiohttp,vaskalas/aiohttp,jashandeep-sohi/aiohttp,singulared/aiohttp,esaezgil/aiohttp,alex-eri/aiohttp-1,morgan-del/aiohttp,arthurdarcet/aiohttp,elastic-coders/aiohttp,andyaguiar/aiohttp,KeepSafe/aiohttp,esaezgil/aiohttp,jettify/aiohttp,Insoleet/aiohttp,vaskalas/aiohttp,noodle-learns-programming/aiohttp,z2v/aiohttp,z2v/aiohttp,playpauseandstop/aiohttp,pfreixes/aiohttp,sterwill/aiohttp,pfreixes/aiohttp,decentfox/aiohttp,AraHaanOrg/aiohttp,esaezgil/aiohttp,decentfox/aiohttp,Eyepea/aiohttp,hellysmile/aiohttp,juliatem/aiohttp,singulared/aiohttp,jashandeep-sohi/aiohttp,mind1master/aiohttp,Srogozins/aiohttp,jashandeep-sohi/aiohttp,vedun/aiohttp,alunduil/aiohttp,panda73111/aiohttp,alex-eri/aiohttp-1,mind1master/aiohttp,pathcl/aiohttp,decentfox/aiohttp,rutsky/aiohttp,AraHaanOrg/aiohttp,elastic-coders/aiohttp,arthurdarcet/aiohttp,danielnelson/aiohttp,mind1master/aiohttp,moden-py/aiohttp,alex-eri/aiohttp-1