BUG: Delete attrs before firing callbacks.
BUG: Delete attrs before firing callbacks.

Prevents failures to remove sqlite files when cleaning up temporary
directories.

magne-max/zipline-ja,enigmampc/catalyst,quantopian/zipline,Scapogo/zipline,bartosh/zipline,bartosh/zipline,Scapogo/zipline,alphaBenj/zipline,wilsonkichoi/zipline,quantopian/zipline,florentchandelier/zipline,humdings/zipline,magne-max/zipline-ja,humdings/zipline,florentchandelier/zipline,wilsonkichoi/zipline,alphaBenj/zipline,enigmampc/catalyst