gccrs: Remove Rust::Optional in favor of tl::optional

gccrs: Remove Rust::Optional in favor of tl::optional

gcc/rust/ChangeLog:

	* Make-lang.in: Remove rust-optional-test.cc's object file
	* ast/rust-macro.h: Remove use of Rust::Optional
	* backend/rust-compile-base.cc
	(HIRCompileBase::resolve_method_address): Likewise.
	* checks/errors/privacy/rust-privacy-reporter.cc
	(PrivacyReporter::check_for_privacy_violation): Likewise.
	(PrivacyReporter::visit): Likewise.
	* checks/errors/privacy/rust-privacy-reporter.h: Likewise.
	* checks/errors/rust-feature-gate.cc (FeatureGate::check): Likewise.
	* checks/errors/rust-feature.cc (Feature::create): Likewise.
	(Feature::as_name): Likewise.
	* checks/errors/rust-feature.h: Likewise.
	* expand/rust-macro-builtins.cc: Likewise.
	* lex/rust-lex.cc (Lexer::Lexer): Likewise.
	(Lexer::skip_token): Likewise.
	(Lexer::dump_and_skip): Likewise.
	* lex/rust-lex.h: Likewise.
	* resolve/rust-ast-resolve-path.cc (ResolvePath::resolve_path): Likewise.
	* resolve/rust-ast-resolve-type.cc (ResolveRelativeTypePath::go): Likewise.
	* rust-lang.cc (run_rust_tests): Likewise.
	* rust-session-manager.cc (Session::compile_crate): Likewise.
	(TargetOptions::dump_target_options): Likewise.
	* rust-session-manager.h (struct TargetOptions): Likewise.
	* util/rust-hir-map.cc (Mappings::lookup_module_children): Likewise.
	(Mappings::lookup_module_chidren_items): Likewise.
	(Mappings::lookup_module_child): Likewise.
	(Mappings::lookup_parent_module): Likewise.
	* util/rust-hir-map.h (RUST_HIR_MAP_H): Likewise.
	* util/rust-optional-test.cc: Removed.
	* util/rust-optional.h: Removed.