chore: remove previous code

note: since the NEW_TA_TASKS feature flag is not enabled for any repos
we're safe to remove the ta_* tasks since they aren't being queued up
anywhere in the old version of the code anyways

this commit removes the TA finisher tasks and replaces the call to
queue those up in the upload task with a call to queue up a separate
chain of processor tasks with the new_impl kwarg set to True. We can
pass this extra kwarg because the processor task has **kwargs which
makes it so even old versions of the code are compatible with this
version of the upload task

until we have the new implementation of the processor task deployed
we should not enable NEW_TA_TASKS since it will possibly cause
duplicate TA uploads to be processed