Don't check for Template:Extension_DPL during update

The check causes MediaWiki to execute some code that depends on some
updates having been run, which is no good.

Backporting because people complain about it a lot.

Bug: 60492
Change-Id: I4305eb1db19005aa09c6ea76086f402aba41bade
(cherry picked from commit d9cd11826ef3bdb206a7ac3f39ce3d09d9240dcb)