Allow PSSH data to be unspecified on license renewal

Currently the CDM requires the caller to specify init data both on key
generation and renewal requests. With this change the CDM relaxes
this requirement for renewals.

Bug: 8732893

Merge of https://widevine-internal-review.googlesource.com/#/c/5322/
from Widevine CDM repo

Change-Id: Idf4ad2bdb20023da4f30bc369ed87eb811c1c4d9

libwvdrmengine/cdm/test/request_license_test.cpp

@@ -62,9 +62,10 @@ class WvCdmRequestLicenseTest : public testing::Test {
   }
 
   void GenerateRenewalRequest(const std::string& key_system,
-                              const std::string& init_data) {
+                              const std::string& not_used) {
     // TODO application makes a license request, CDM will renew the license
     // when appropriate.
+    std::string init_data;
     wvcdm::CdmAppParameterMap app_parameters;
     std::string server_url;
     EXPECT_EQ(decryptor_.GenerateKeyRequest(session_id_,