ntlm: Remove unnecessary casts in readshort_le()

I don't think both of my fix ups from yesterday were needed to fix the
compilation warning, so remove the one that I think is unnecessary and
let the next Android autobuild prove/disprove it.

lib/curl_ntlm_msgs.c

@@ -166,8 +166,8 @@ static unsigned int readint_le(unsigned char *buf)
  */
 static unsigned short readshort_le(unsigned char *buf)
 {
-  return (unsigned short)((unsigned short)((unsigned short)buf[0]) |
-                          (unsigned short)((unsigned short)buf[1] << 8));
+  return (unsigned short)(((unsigned short)buf[0]) |
+                          ((unsigned short)buf[1] << 8));
 }
 
 /*