[chore, plugin] Simplify Wallabag http.request handling (#6307)
[chore, plugin] Simplify Wallabag http.request handling (#6307)

See <https://github.com/koreader/koreader-base/issues/594#issuecomment-484233915>.

LuaSocket takes care of everything now, so all similar code can be simplified.
poire-z/koreader,koreader/koreader,poire-z/koreader,Frenzie/koreader,Hzj-jie/koreader,mwoz123/koreader,koreader/koreader,Frenzie/koreader,Markismus/koreader,NiLuJe/koreader,NiLuJe/koreader,pazos/koreader