streaming: Fix Assertion _instances.empty() failed
streaming: Fix Assertion _instances.empty() failed

seastar: ./core/sharded.hh:227: seastar::sharded<Service>::~sharded()
[with Service = streaming::stream_session::handler]: Assertion
`_instances.empty()' failed.

wildinto/scylla,raphaelsc/scylla,senseb/scylla,tempbottle/scylla,gwicke/scylla,dwdm/scylla,eklitzke/scylla,bowlofstew/scylla,rentongzhang/scylla,gwicke/scylla,scylladb/scylla,aruanruan/scylla,eklitzke/scylla,tempbottle/scylla,justintung/scylla,capturePointer/scylla,avikivity/scylla,glommer/scylla,phonkee/scylla,gwicke/scylla,linearregression/scylla,rentongzhang/scylla,dwdm/scylla,phonkee/scylla,acbellini/scylla,scylladb/scylla,kjniemi/scylla,phonkee/scylla,kangkot/scylla,linearregression/scylla,victorbriz/scylla,asias/scylla,capturePointer/scylla,stamhe/scylla,guiquanz/scylla,wildinto/scylla,shaunstanislaus/scylla,kangkot/scylla,scylladb/scylla,senseb/scylla,rluta/scylla,tempbottle/scylla,acbellini/scylla,bowlofstew/scylla,aruanruan/scylla,aruanruan/scylla,bowlofstew/scylla,respu/scylla,wildinto/scylla,shaunstanislaus/scylla,victorbriz/scylla,shaunstanislaus/scylla,stamhe/scylla,glommer/scylla,avikivity/scylla,avikivity/scylla,kjniemi/scylla,victorbriz/scylla,justintung/scylla,duarten/scylla,justintung/scylla,glommer/scylla,capturePointer/scylla,dwdm/scylla,raphaelsc/scylla,respu/scylla,kangkot/scylla,duarten/scylla,asias/scylla,rluta/scylla,linearregression/scylla,duarten/scylla,respu/scylla,acbellini/scylla,senseb/scylla,raphaelsc/scylla,guiquanz/scylla,asias/scylla,scylladb/scylla,rentongzhang/scylla,rluta/scylla,guiquanz/scylla,stamhe/scylla,kjniemi/scylla,eklitzke/scylla