Don't warn finishing ops for gone packages

We finish ops when packages get removed to guarantee no dangling
started ops. However, some part of the system may asynchronously
finish ops for an already gone package. Hence, finishing an op
for a non existing package is fine and we don't log as a wtf.

Test: manual

bug:75436227

Change-Id: I33156d3f999f671ea65a70b485dac8afd4639b42