docs: GetDataDirNet and GetDataDirBase don't create datadir

Since #27073, the behaviour of GetDataDir changed to only return
the datadir path, but not create it. This also changed the behaviour
of GetDataDirNet and GetDataDirBase but the docs do not yet reflect
that.

Author: stickies-v

src/util/system.h

@@ -287,15 +287,13 @@ class ArgsManager
      * Get data directory path
      *
      * @return Absolute path on success, otherwise an empty path when a non-directory path would be returned
-     * @post Returned directory path is created unless it is empty
      */
     const fs::path& GetDataDirBase() const { return GetDataDir(false); }
 
     /**
      * Get data directory path with appended network identifier
      *
      * @return Absolute path on success, otherwise an empty path when a non-directory path would be returned
-     * @post Returned directory path is created unless it is empty
      */
     const fs::path& GetDataDirNet() const { return GetDataDir(true); }