We don't need this any more.

This was used when external references used hidden sheets as a cheesy
workaround.

Change-Id: I7e4bf3a2235a0c2e80d0aa71a81f22a10b8d0fd5
Pre-quote sheet names to avoid doing it every single time.

Change-Id: Ib103ca22bf59c334945c0462588610899a0acfaa