Simplify empty parameter pack regression

Reduce the regression case to a single abbreviated template function called with empty and non-empty packs while retaining the expected restrictionPack alert.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jketema

cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticVariables/UnusedStaticVariables.expected

@@ -2,4 +2,4 @@
 | test.cpp:8:12:8:21 | staticVar6 | Static variable staticVar6 is never read. |
 | test.cpp:10:11:10:19 | constVar8 | Static variable constVar8 is never read. |
 | test.cpp:12:12:12:22 | staticVar10 | Static variable staticVar10 is never read. |
-| test.cpp:68:58:68:72 | restrictionPack | Static variable restrictionPack is never read. |
+| test.cpp:53:25:53:39 | restrictionPack | Static variable restrictionPack is never read. |

cpp/ql/test/query-tests/Best Practices/Unused Entities/UnusedStaticVariables/test.cpp

@@ -50,29 +50,12 @@ struct WithDestructor
 static WithConstructor constructed; // GOOD (constructor has a side effect)
 static WithDestructor destructed; // GOOD (destructor has a side effect)
 
-template <typename From, typename To>
-concept ConvertibleTo = requires(From value) { static_cast<To>(value); };
-
-struct Store
-{
-	using LinkAddressType = unsigned;
-	struct LinkType
-	{
-		LinkAddressType restriction;
-	};
-};
-
-template <typename TStore>
-static auto All(
-	const TStore&,
-	ConvertibleTo<typename TStore::LinkAddressType> auto... restrictionPack) // $ SPURIOUS: Alert
+static auto All(auto... restrictionPack) // $ SPURIOUS: Alert
 {
-	typename TStore::LinkType restriction{static_cast<typename TStore::LinkAddressType>(restrictionPack)...};
-	return restriction;
+	return (0U + ... + static_cast<unsigned>(restrictionPack));
 }
 
 int main()
 {
-	Store store;
-	return All(store).restriction + All(store, 2U).restriction;
+	return All() + All(2U);
 }