[C#] Remove redundant ToString() methods.

Author: mjpt777

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/csharp/CSharpGenerator.java

@@ -1789,10 +1789,11 @@ private CharSequence generateChoiceDisplay(final String enumName)
  append(sb, TWO_INDENT, "internal static void BuildString(this " + enumName + " val, StringBuilder builder)");
  append(sb, TWO_INDENT, "{");
  Separators.BEGIN_SET.appendToGeneratedBuilder(sb, THREE_INDENT);
- append(sb, THREE_INDENT, "builder.Append(val.ToString());");
+ append(sb, THREE_INDENT, "builder.Append(val);");
  Separators.END_SET.appendToGeneratedBuilder(sb, THREE_INDENT);
  append(sb, TWO_INDENT, "}");
  append(sb, INDENT, "}");
+
  return sb;
  }