[audio] Remove getInputForAttr usage test

This test attempts to validate that getInputForAttr fails when being
passed system usages, however, system usages are only relevant for
outputs, not inputs, so this test is malformed.

Test: atest AudioSystemUsageTest
Bug: 374870131
Fixes: 379983123
Flag: EXEMPT TEST_ONLY
Change-Id: Ic27c91c2286ebe7b68f9cfa01fc9bcc3feb3c483