Allow Unprovisioning of Origins

(This is a merge of http://go/wvgerrit/14051)

Adds support for passing a special provisioning response ("delete")
to the provisioning API in order to unprovision the current origin.
Note that the origin MUST be set or else this will fail.

The existing, system-only unprovisionDevice() method is unaffected.

Bug: 12247651
Change-Id: I16d296397d8e9e73c8f43e36c86838873318a398

libwvdrmengine/mediadrm/include/WVDrmPlugin.h

@@ -276,6 +276,8 @@ class WVDrmPlugin : public android::DrmPlugin,
 
   bool InitDataResemblesPSSH(const Vector<uint8_t>& initData);
 
+  status_t unprovision(const std::string& origin);
+
   const char* determineOrigin() const;
 };