R1:106e90dcf086

Remove the "willApplyTransactions()" hook from ApplicationTransactionEditor

Summary:
Depends on D19908. Ref T13222. In D19897, I reordered some transaction code and affected the call order of `willApplyTransactions()`.

It turns out that we use this call for only one thing, and that thing is pretty silly: naming the raw paste data file when editing paste content.

This is only user-visible in the URL when you click "View Raw Paste" and seems exceptionally low-value, so remove the hook and pick a…