OEMCrypto_DeleteUsageTable now returns OEMCrypto_SUCCESS

Copy of widevine change:
https://widevine-internal-review.googlesource.com/#/c/10911/

OEMCrypto_DeleteUsageTable used to return an error on every call
because UsageTable::Clear always returned false.  Since there is no
error checking that Clear can do, its return type has been changed to
void, and DeleteUsageTable now returns OEMCrypto_SUCCESS for all
calls.

bug: 16799906
Change-Id: Iaa2f572e4b0feb554877579596a7f43a64d20954

libwvdrmengine/oemcrypto/mock/src/oemcrypto_usage_table_mock.h

@@ -86,7 +86,7 @@ class UsageTable {
   OEMCryptoResult UpdateTable();
   OEMCryptoResult DeactivateEntry(const std::vector<uint8_t> &pst);
   bool DeleteEntry(const std::vector<uint8_t> &pst);
-  bool Clear();
+  void Clear();
 
  private:
   UsageTableEntry *FindEntryLocked(const std::vector<uint8_t> &pst);