Revert "Maintain file order when iterating wikiversions.json"

Apparently testwiki is the only wiki version that creates a
proper ExtensionMessages file which means this hack doesn't
help.

This reverts commit 7d47ace90f60bb372f68337eccb79f68fe6b2653.

Bug: 63659
Change-Id: I610970967071bf37dfba3cdba3d42c31424f740f