Make CdmProvisioningResponse const and DeviceFiles level support

* Make CdmProvisioningResponse const.

  [ Merge of http://go/wvgerrit/14618 ]

  The lack of const on this reference seems to be a mistake, since the
  responses is never modified.  This also allows the new CE CDM to pass
  responses directly through from the caller.

* Let Properties determine DeviceFiles level support

  [ Merge of http://go/wvgerrit/14620 ]

  Non-Android platforms do not have multiple security levels, and so do
  not use the security level to construct a base path.

  Instead of requiring a known "security level" to construct a file,
  accept anything that platform Properties will accept as a base path.

* Drop Properties::GetSecurityLevel().

  [ Merge of http://go/wvgerrit/14617 ]

  This seems to be dead code.

Change-Id: I94a970279213100730d6e6c763558dbe386f936a

libwvdrmengine/cdm/core/src/cdm_engine.cpp

@@ -589,7 +589,7 @@ CdmResponseType CdmEngine::GetProvisioningRequest(
  * Returns NO_ERROR for success and  CdmResponseType error code if fails.
  */
 CdmResponseType CdmEngine::HandleProvisioningResponse(
-    const std::string& origin, CdmProvisioningResponse& response,
+    const std::string& origin, const CdmProvisioningResponse& response,
     std::string* cert, std::string* wrapped_key) {
   if (response.empty()) {
     LOGE("CdmEngine::HandleProvisioningResponse: Empty provisioning response.");