Implement Method to Release Licenses Without a Server Roundtrip

Merge from Widevine repo of http://go/wvgerrit/52480

Partners have asked for a way to release offline licenses without
using a release message. This is typically used by cable partners who
are caching licenses ahead of time and do not care about usage
statistics.

As part of implementing this request, CdmSession::DeleteLicense() was
renamed to reflect that it only deletes the *files* associated with a
license, and a new CdmSession::DeleteLicense() has been written that
also cleans up other related data.

Bug: 77955334
Test: CE CDM Unit Tests
Test: tested as part of http://go/ag/4674759
Change-Id: I00d6e20935c5fecb3ac9be6757c0f191d85c6bd6

libwvdrmengine/cdm/core/include/cdm_session.h

@@ -153,8 +153,13 @@ class CdmSession {
   // preferable to simply delete this object rather than call this method.
   virtual CdmResponseType RemoveKeys();
 
-  // Delete current license and matching usage record
-  bool DeleteLicense();
+  // Remove the current offline license and/or matching usage record, if any
+  // exist.
+  CdmResponseType RemoveLicense();
+  // Delete this session's associated license or usage record file. Note that,
+  // unlike RemoveLicense(), this method ONLY affects the file system and does
+  // not touch the usage table headers.
+  bool DeleteLicenseFile();
 
   // Generate unique ID for each new session.
   CdmSessionId GenerateSessionId();