Replace use of boost::trim_right with locale-independent TrimString

Note the only use of readStdin is fed to DecodeHexTx, which fails in
IsHex on non-hex characters as recorded in p_util_hexdigit.

src/bitcoin-tx.cpp

@@ -772,9 +772,7 @@ static std::string readStdin()
     if (ferror(stdin))
         throw std::runtime_error("error reading stdin");
 
-    boost::algorithm::trim_right(ret);
-
-    return ret;
+    return TrimString(ret);
 }
 
 static int CommandLineRawTx(int argc, char* argv[])