core: remove unused code
core: remove unused code

(clientid doesn't exist in foldersync requests)

Signed-off-by: Etienne CHAMPETIER <d24370f93c848f9b9e9043ebb082d433901eaa60@fiducial.net>

RavenB/Z-Push-contrib,Freeaqingme/Z-Push-contrib,fmbiete/Z-Push-contrib,mta59066/Z-Push-contrib