Remove dedicated TextCodecUTF16

LayoutTests/fast/encoding/char-decoding-truncated.html

Index: LayoutTests/fast/encoding/char-decoding-truncated.html
diff --git a/LayoutTests/fast/encoding/char-decoding-truncated.html b/LayoutTests/fast/encoding/char-decoding-truncated.html
index 9e6c05df16cb58bcf522a72720c8c1e9dbbab3b7..9533e4df2386819bad210c9b69b9edd934691a67 100644
--- a/LayoutTests/fast/encoding/char-decoding-truncated.html
+++ b/LayoutTests/fast/encoding/char-decoding-truncated.html
@@ -12,13 +12,13 @@ testDecode('utf-8', '%E2', 'U+FFFD');
 
 // UTF-16 codec does not emit replacement characters
 testDecode('utf-16', '%69%D8%D6%DE', 'U+D869/U+DED6');
-testDecode('utf-16', '%69%D8%D6', 'U+D869');
-testDecode('utf-16', '%69%D8', 'U+D869');
-testDecode('utf-16', '%69', '');
+testDecode('utf-16', '%69%D8%D6', 'U+FFFD');
+testDecode('utf-16', '%69%D8', 'U+FFFD');
+testDecode('utf-16', '%69', 'U+FFFD');
 testDecode('utf-16be', '%D8%69%DE%D6', 'U+D869/U+DED6');
-testDecode('utf-16be', '%D8%69%DE', 'U+D869');
-testDecode('utf-16be', '%D8%69', 'U+D869');
-testDecode('utf-16be', '%D8', '');
+testDecode('utf-16be', '%D8%69%DE', 'U+FFFD');
+testDecode('utf-16be', '%D8%69', 'U+FFFD');
+testDecode('utf-16be', '%D8', 'U+FFFD');
 
 // Other codecs emit replacement characters
 testDecode('gb2312', '%A3%A0', 'U+3000');