doc: simplify the description for StringDecoder

Author: pluris

doc/api/string_decoder.md

@@ -63,8 +63,7 @@ Creates a new `StringDecoder` instance.
 added: v0.9.3
 -->
 
-* `buffer` {string|Buffer|TypedArray|DataView} A `string`, or `Buffer`, or
-  `TypedArray`, or `DataView` containing the bytes to decode.
+* `buffer` {string|Buffer|TypedArray|DataView} The bytes to decode.
 * Returns: {string}
 
 Returns any remaining input stored in the internal buffer as a string. Bytes
@@ -86,8 +85,7 @@ changes:
                  character instead of one for each individual byte.
 -->
 
-* `buffer` {string|Buffer|TypedArray|DataView} A `string`, or `Buffer`, or
-  `TypedArray`, or `DataView` containing the bytes to decode.
+* `buffer` {string|Buffer|TypedArray|DataView} The bytes to decode.
 * Returns: {string}
 
 Returns a decoded string, ensuring that any incomplete multibyte characters at