hg: write narrow patterns after repo creation Now that hg.clone() knows when a narrow clone is requested, it makes sense to have it update the narrow patterns for the repo soon after the repo is created, before any exchange occurs. Previously, the narrow extension was monkeypatching an exchange function to do this. The old code is redundant and has been removed. Differential Revision: https://phab.mercurial-scm.org/D4541