rev: move sqlite_t type alias into class

changes per #522 (comment)

include/geopackage/NGen_SQLite.hpp

@@ -19,11 +19,6 @@ struct sqlite_deleter
     void operator()(sqlite3_stmt* stmt) { sqlite3_finalize(stmt); }
 };
 
-/**
- * Smart pointer (unique) type for sqlite3 database
- */
-using sqlite_t = std::unique_ptr<sqlite3, sqlite_deleter>;
-
 /**
  * Smart pointer (shared) type for sqlite3 prepared statements
  */
@@ -157,6 +152,11 @@ inline T sqlite_iter::get(const std::string& name) const
 class sqlite
 {
   private:
+    /**
+     * Smart pointer (unique) type for sqlite3 database
+     */
+    using sqlite_t = std::unique_ptr<sqlite3, sqlite_deleter>;
+
     sqlite_t conn = nullptr;
     stmt_t   stmt = nullptr;