No-op an ancient Paste edge migration which no longer functions after a database rename

Summary:
Fixes T13510. This migration currently fails because it tries to affect the "paste" database, but when it runs this database will be named "pastebin".

Since the cost of fixing it in place or moving it past the rename migration both seem relatively high (and the cost of throwing it away is plausibly zero) just throw it for now.

Test Plan: Looked at file, saw no more code that can execute.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13510

Differential Revision: https://secure.phabricator.com/D21132