remove deprecated type 'GenesisConfig' (#3378)

# Description

Removed deprecated type `GenesisConfig` from the codebase.

Closes https://github.com/paritytech/polkadot-sdk/issues/175

# Checklist

- [x] My PR includes a detailed description as outlined in the
"Description" section above
- [x] My PR follows the [labeling requirements](CONTRIBUTING.md#Process)
of this project (at minimum one label for `T`
  required)
- [x] I have made corresponding changes to the documentation (if
applicable)

---------

Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>
Co-authored-by: Michal Kucharczyk <1728078+michalkucharczyk@users.noreply.github.com>

substrate/frame/support/procedural/src/construct_runtime/expand/config.rs

@@ -76,10 +76,6 @@ pub fn expand_outer_config(
 			#fields
 		}
 
-		#[cfg(any(feature = "std", test))]
-		#[deprecated(note = "GenesisConfig is planned to be removed in December 2023. Use `RuntimeGenesisConfig` instead.")]
-		pub type GenesisConfig = RuntimeGenesisConfig;
-
 		#[cfg(any(feature = "std", test))]
 		impl #scrate::sp_runtime::BuildStorage for RuntimeGenesisConfig {
 			fn assimilate_storage(

substrate/frame/support/test/tests/construct_runtime_ui/deprecated_where_block.stderr

@@ -347,7 +347,7 @@ error[E0277]: the trait bound `Runtime: Config` is not satisfied
 26 |         System: frame_system::{Pallet, Call, Storage, Config<T>, Event<T>},
    |         ^^^^^^ the trait `Config` is not implemented for `Runtime`
    |
-note: required by a bound in `frame_system::GenesisConfig`
+note: required by a bound in `GenesisConfig`
   --> $WORKSPACE/substrate/frame/system/src/lib.rs
    |
    |     pub struct GenesisConfig<T: Config> {