Memory exhaustion on large delete

Problem/Motivation

Out of memory error when deleting a large batch of redirects.

Steps to reproduce

I imported about 15K redirects out of a batch of 86K. I realized the fields were in the wrong order, and stopped the import.
When I attempted to delete with the same file of approximately 86K records, the delete process failed with an out of memory error.

Proposed resolution

Process deletes in a batch, the same way it processes imports, or otherwise reduce the batch numbers so it doesn't run out of memory.

My PHP memory limit is already 512MB, so you could probably get it to fail with a lot fewer than 86K records.