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/Android.bp

@@ -195,7 +195,6 @@ cc_library_static {
         "cdm/src/timer.cpp",
         "cdm/util/src/cdm_random.cpp",
         "cdm/util/src/clock.cpp",
-        "cdm/util/src/error_string_util.cpp",
         "cdm/util/src/file_store.cpp",
         "cdm/util/src/file_utils.cpp",
         "cdm/util/src/log.cpp",