QUtf8Codec: Remove dead code

The maximum value for charsNeeded is 4, so if bytesAvailable is less
than charsNeeded - 1, the it's at most 2. It can't be larger than 2.

Found by Coverity, CID 11000.

Change-Id: I42e7ef1a481840699a8dffff1407ef9221a4fd80
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

src/corelib/codecs/qutfcodec_p.h

@@ -217,8 +217,6 @@ namespace QUtf8Functions
                 return Traits::Error;
             if (bytesAvailable > 1 && !isContinuationByte(Traits::peekByte(src, 1)))
                 return Traits::Error;
-            if (bytesAvailable > 2 && !isContinuationByte(Traits::peekByte(src, 2)))
-                return Traits::Error;
             return Traits::EndOfString;
         }