Rename and update metadata of rfc 3114 - prelude_2021.

Author: m-ou-se

text/0000-prelude-2021-traits.md renamed to text/3114-prelude-2021.md

@@ -1,7 +1,7 @@
-- Feature Name: `prelude_2021_traits`
+- Feature Name: `prelude_2021`
 - Start Date: 2021-02-16
-- RFC PR: [rust-lang/rfcs#0000](https://github.com/rust-lang/rfcs/pull/0000)
-- Rust Issue: [rust-lang/rust#0000](https://github.com/rust-lang/rust/issues/0000)
+- RFC PR: [rust-lang/rfcs#3114](https://github.com/rust-lang/rfcs/pull/3114)
+- Rust Issue: [rust-lang/rust#85684](https://github.com/rust-lang/rust/issues/85684)
 
 # Summary
 [summary]: #summary