Fix cens Mode in Android CDM

(This is a merge of go/wvgerrit/20500)

This patch removes the logic that calculates the "pattern offset" from
the Android glue layer. There is no such thing as a pattern offset, and
setting this value to anything other than zero may break cens mode on
some devices.

To reduce the risk of setting this value to anything other than zero,
the offset_blocks parameter has been removed from the pattern descriptor
in the CDM Core. It will have to remain part of OEMCrypto v11,
unfortunately, but the code to set it to zero is now centralized in
CryptoSession.

Bug: 28726863
Change-Id: I9c5bfe470fe251c7a57901dc2e998f4dab7fe7d7

libwvdrmengine/cdm/core/include/wv_cdm_types.h

@@ -282,11 +282,9 @@ enum CdmCipherMode {
 struct CdmCencPatternEncryptionDescriptor {
   size_t encrypt_blocks;  // number of 16 byte blocks to decrypt
   size_t skip_blocks;     // number of 16 byte blocks to leave in clear
-  size_t offset_blocks;   // offset into the pattern for this call, in blocks
   CdmCencPatternEncryptionDescriptor()
       : encrypt_blocks(0),
-        skip_blocks(0),
-        offset_blocks(0) {}
+        skip_blocks(0) {}
 };
 
 struct CdmDecryptionParameters {