Remove RandomNumberGenerator (#9198)

* Remove RandomNumberGenerator

This is not used in Substrate/Polkadot. If someone else needs it, they
can copy the code or use chacha.

* 🤦

substrate/primitives/runtime/src/lib.rs

@@ -54,7 +54,6 @@ pub mod offchain;
 pub mod testing;
 pub mod traits;
 pub mod transaction_validity;
-pub mod random_number_generator;
 mod runtime_string;
 mod multiaddress;
 pub mod runtime_logger;
@@ -85,8 +84,6 @@ pub use sp_arithmetic::helpers_128bit;
 /// Re-export big_uint stuff.
 pub use sp_arithmetic::biguint;
 
-pub use random_number_generator::RandomNumberGenerator;
-
 pub use either::Either;
 
 /// An abstraction over justification for a block's validity under a consensus algorithm.