Silence API warnings introduced by a85e817d

Silence API warnings introduced by a85e817d

a85e817d is a slightly breaking API change to classes that were
technically public and technically released in 4.0. However, it is
highly unlikely that people were actually depending on public behavior,
since there were no public methods to create PushCertificates with
anything other than null field values, or a PushCertificateParser that
did anything other than infinite loop or throw exceptions when reading.

Change-Id: I1d0ba9ea0a347e8ff5a0f4af169d9bb18c5838d2
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>