Avoid fmt when constructor already does it

There is a correctnes issue here, but #3724 will fix that. This is just
a cleanup for brevity's sake.

src/libstore/sqlite.hh

@@ -96,10 +96,20 @@ struct SQLiteTxn
 };
 
 
-MakeError(SQLiteError, Error);
-MakeError(SQLiteBusy, SQLiteError);
+struct SQLiteError : Error
+{
+    const char *path;
+    int errNo, extendedErrNo;
 
-[[noreturn]] void throwSQLiteError(sqlite3 * db, const FormatOrString & fs);
+    template<typename... Args>
+    [[noreturn]] static void throw_(sqlite3 * db, const std::string & fs, const Args & ... args);
+
+protected:
+    template<typename... Args>
+    SQLiteError(const char *path, int errNo, int extendedErrNo, const Args & ... args);
+};
+
+MakeError(SQLiteBusy, SQLiteError);
 
 void handleSQLiteBusy(const SQLiteBusy & e);