Rename `interestingArgv` to `explicitArgv`.

Summary: `interestingArgv` isn't a very useful name, see D9607#45.

Test Plan: N/A

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9617