Remove unnecessary duplication in generic asset create (#4744)

* Remove unneccessary duplication in generic asset create

* Increment impl_version due to refactoring generic_asset

substrate/bin/node/runtime/src/lib.rs

@@ -81,7 +81,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	// implementation changes and behavior does not, then leave spec_version as
 	// is and increment impl_version.
 	spec_version: 207,
-	impl_version: 207,
+	impl_version: 208,
 	apis: RUNTIME_API_VERSIONS,
 };