Remove ObjectStreamClass workarounds for API > 24

Commit 987c9cae added
back private API that was abused by some apps. This change
makes
- ObjectStreamClass.getConstructorId(Class<?>)
- ObjectStreamClass.newInstance(Class<?>, long)
throw UnsupportedOperationException if called
with targetSdkVersion > 24.

Change-Id: I79234ca718991ba9dc73b7577768b617de9ad7df
Test: org.apache.harmony.tests.java.io.ObjectStreamClassTest
Bug: 28283540