Delete operations should parse queries without holding locks, when possible.

In SERVER-10159/SERVER-12380, the update paths were modified to parse queries outside the write lock, when possible. This improves concurrency among writes, and between reads and writes, by minimizing time spent with data locks held.

The same optimization could be applied to the delete path in a straightforward way. See the implementation of the UpdateExecutor and its use in the BatchWriteExecutor for example.