Revert "Fix MediaDrm security level APIs"

This reverts commit 6a5934ae.


Reason for revert: Build cop here. The CL topic that I'm reverting broke several builds: Drm.h's openSession(Vector<uint8_t> &sessionId) hides overloaded virtual function openSession(DrmPlugin::SecurityLevel securityLevel, ..) from IDrm.h.

https://android-build.googleplex.com/builds/submitted/4598692/full-eng/latest/view/logs/build_error.log

Change-Id: I8a1ce95ca6f48bec6c46f84a0fef7a48f975c406