Removing num_children from storage/jellyfish-merkle/src/node_type/mod.rs
Removing num_children from storage/jellyfish-merkle/src/node_type/mod.rs

Closes: #4219
Approved by: bmwill

aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core