Remove some obsolete lint and unit support

Summary:
Ref T8096.

Long ago, support for "postponed" lint and unit tests got hacked in. arc would publish a bunch of ghost results, and then something else would fill the results in later.

This was always a hack. It is not nearly as powerful or flexible as having a real build system, and is obsolete with Harbormaster, which supports these operations in a more reasonable and straightforward way.

This was used (only? almost only?) at Facebook.

• Remove differential.finishpostponedlinters. This only served to update postponed linters.
• Remove lint magic in differential.setdiffproperty. This magic only made sense in the context of postponed linters.
• Remove differential.updateunitresults. The only made sense for postponed unit tests.

And one minor change: when a diff contains >100 affected files, we hide the content by default, but show content for files with inline comments. Previously, we'd do this for lint inlines, too. I don't tink this is too useful, and it's much simpler to just remove it. We could add it back at some point, but I think large changes often trigger a lot of lint and no one actually cares. The behavior for actual human inlines is retained.

Test Plan: grep

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T8096

Differential Revision: https://secure.phabricator.com/D13848