Fix using result of method (void)
Summary:
`PhabricatorAuthSessionEngine::signLegalpadDocuments()` and `PhutilTestCase::tryTestCaseMap()` return void.
Thus do not assign this result to a variable as that variable is not used in the further code anyway.
Just call the method on its own line.
Test Plan: Run static code analysis (PHPStan).
Reviewers: O1 Blessed Committers, mainframe98
Reviewed By: O1 Blessed Committers, mainframe98
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D26309