UDL can't have a Remote enums with fields

[mhammond]

Eg, a simple enum:

uniffi-rs/fixtures/ext-types/lib/src/ext-types-lib.udl

Lines 71 to 75 in 4cbb8f1

	[Remote, NonExhaustive]
	enum ExternalCrateNonExhaustiveEnum {
	"One",
	"Two",
	};

If we had an enum with fields, we'd need an [Enum, Remote] interface {... }, but that would fail -

uniffi-rs/uniffi_udl/src/attributes.rs

Line 458 in aa200a6

// If `[Enum]` is specified it must be the only attribute.

via #2334