folder_block_manager_test: make sure deleted blocks are uncached
folder_block_manager_test: make sure deleted blocks are uncached

Issue: KBFS-749

keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs