Remove unused configurations

[vldm]

Configuration like: https://docs.rs/rstml/latest/rstml/struct.ParserConfig.html#method.type_of_top_level_nodes
https://docs.rs/rstml/latest/rstml/struct.ParserConfig.html#method.number_of_top_level_nodes
are not look very reusable.
Instead macro implementor can always apply those checks manually.

there also https://docs.rs/rstml/latest/rstml/struct.ParserConfig.html#method.flat_tree
that looks usable only for debug, but i propose to keep it for now, because it's implementation require some knowledge of types.