ref: remove workarounds for package_revise

[paulmueller]

Hopefully, after these are fixed, the codebase will be a little cleaner:

DCOR-dev/DCOR-Aid#28
ckan/ckan#6472
ckan/ckan#2949

[paulmueller]

Specifically talking about IPackageController.after_update which also messes with the tests.

[paulmueller]

Everything is now in IPackageController.after_dataset_update with a check for background jobs.