Move HiddenApiTest from src to src/java

The java files have recently been moved to src/java in order to have
both java and native source files under src. However, HiddenApiTest.java
wasn't moved then. Fixing the error.

Test: atest  CtsHiddenApiDiscoveryTestCases The test runs.
Change-Id: Idcb1432071552e41611bce298a7ba876edb1be73
3 files changed