Remove expensive, pointless typeachecking in custom fields
Summary:
Ref T11404. On my system, this improves performance by 10-15% for `differential.revision.search`.
`PhutilTypeSpec` provides high quality typechecking and is great for user-facing things that need good error messages.
However, it's also a bit slow, and pointless here (the API is internal and it only has one possible option).
I think I added this after writing `checkMap` just because I wanted to use it more often. My desire is sated after finding many reasonable ways to use it to give users high-quality error messages about things like configuration files.
Test Plan: Profiled `differential.revision.search` before and after change, saw wall time drop from ~220ms to ~195ms.
Reviewers: yelirekim, chad
Reviewed By: chad
Maniphest Tasks: T11404
Differential Revision: https://secure.phabricator.com/D16354