Moved OEMCryptoResult string converter.

[ Merge of http://go/wvgerrit/170073 ]

Removed the file "error_string_util.cpp" and its header, moving the
OEMCryptoResult to string converter to "wv_cdm_types.cpp".  This extra
file served little purpose, and created a dependency on the CDM utils
to the CDM itself.

This is part of the effort to fix the formatting of WV metrics; making
enum-to-string conversion uniform throughout the CDM.

Bug: 239462891
Test: adb shell dumpsys android.hardware.drm.IDrmFactory/widevine -m
Test: Manual testing with Google TV
Change-Id: I4bf95d26b623f5b8fa86bdb2578cbc4ee65125cb

libwvdrmengine/cdm/core/include/wv_cdm_types.h

@@ -944,6 +944,9 @@ const char* IdToString(const std::string& id);
 // Some CDM API function allow for optional string parameters to be
 // provided as string pointers.
 const char* IdPtrToString(const std::string* id);
+
+// Logging utilities for OEMCrypto types.
+const char* OemCryptoResultToString(OEMCryptoResult result);
 }  // namespace wvcdm
 
 #endif  // WVCDM_CORE_WV_CDM_TYPES_H_