message: GenEnum: bit_flags: Remove useless conditions
  The conditions to add the "NONE" or "ANY" value in the enum were useless
  because the user cannot provide a zero value or a bitmask (for "ANY") in
  the bit_flags enum type.
diff: @@ -525,16 +525,13 @@ class CppGenerator : public BaseGenerator {
  code_.SetValue("SEP", ",\n");
  if (enum_def.attributes.Lookup("bit_flags")) {
  - if (minv->value != 0) { // If the user didn't defined NONE value
  code_.SetValue("KEY", GenEnumValDecl(enum_def, "NONE"));
  code_.SetValue("VALUE", "0");
  code_ += "{{SEP}} {{KEY}} = {{VALUE}}\\";
  - }
  - if (maxv->value != anyv) { // If the user didn't defined ANY value
  +
  code_.SetValue("KEY", GenEnumValDecl(enum_def, "ANY"));
  code_.SetValue("VALUE", NumToString(anyv));
  code_ += "{{SEP}} {{KEY}} = {{VALUE}}\\";
  - }
  } else { // MIN & MAX are useless for bit_flags
  code_.SetValue("KEY",GenEnumValDecl(enum_def, "MIN"));
  code_.SetValue("VALUE", GenEnumValDecl(enum_def, minv->name));
  