fi-0032: Duplicate modifiers disallowed {:#fi-0032}

Specifying the same modifier in a single declaration is prohibited:

{% include “docs/reference/fidl/language/error-catalog/label/_bad.md” %}

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/bad/fi-0032.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}

Remove the duplicated modifier:

{% include “docs/reference/fidl/language/error-catalog/label/_good.md” %}

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0032.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}