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/util/include/error_string_util.h

@@ -1,11 +0,0 @@
-#ifndef ERROR_STRING_UTIL_H_
-#define ERROR_STRING_UTIL_H_
-
-#include <string>
-
-namespace wvutil {
-
-const std::string OEMCryptoResultToString(int oemcrypto_result);
-
-}  // namespace wvutil
-#endif  // ERROR_STRING_UTIL_H_