Cleanup certificate API extension

Fixes a couple of minor issues with the v2 and v3 versions
of the certificate API extension identified during the
v2->v3 port
* Removes unused CertificatesTemplate class
* Corrects doc strings for a couple of methods

Change-Id: If022d2393ceab5ce7e6311c92a6f52b6325039bc
Merge "Cleanup certificate API extension"