build: Remove obsolete check for vendoring support
build: Remove obsolete check for vendoring support

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GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4008

lkwg82/syncthing,jryans/syncthing,syncthing/syncthing,uok/syncthing,xduugu/syncthing,le9i0nx/syncthing,imsodin/syncthing,jryans/syncthing,uok/syncthing,rumpelsepp/syncthing,uok/syncthing,le9i0nx/syncthing,AudriusButkevicius/syncthing,syncthing/syncthing,nrm21/syncthing,rumpelsepp/syncthing,xduugu/syncthing,xduugu/syncthing,imsodin/syncthing,syncthing/syncthing,wweich/syncthing,nrm21/syncthing,wweich/syncthing,lkwg82/syncthing,nrm21/syncthing,rumpelsepp/syncthing,wweich/syncthing,AudriusButkevicius/syncthing,uok/syncthing,wweich/syncthing,imsodin/syncthing,syncthing/syncthing,jryans/syncthing,syncthing/syncthing,nrm21/syncthing,rumpelsepp/syncthing,lkwg82/syncthing,imsodin/syncthing,xduugu/syncthing,jryans/syncthing,le9i0nx/syncthing,le9i0nx/syncthing,syncthing/syncthing,AudriusButkevicius/syncthing,lkwg82/syncthing,imsodin/syncthing,AudriusButkevicius/syncthing