Remove _views_bulk_operations_operation_do().

This came out of: #1367644: Batch the selecting of all ids on all pages, clean up execution types..

We should remove _views_bulk_operations_operation_do() and execute the operations directly.
That function is just a level of indirection, doing an unneeded access check (since the same check was done when the user was presented with a list of operations at the beginning of the process), and doing a very messy exit.