Cleans up PackageInstaller.Session docs

This change addresses API council feedback by making the
PackageInstaller#Session reference to setMultiPackage() consistent with
the implementation and the method doc.

Fixes: 124326154
Test: atest AtomicInstallTest
Change-Id: I5ef1ebb715ea33a6070ac431c18a9c661b5df00a
1 file changed