fix: Remove issue link

Author: epage

text/3692-feature-unification.md

@@ -1,7 +1,6 @@
 - Feature Name: `feature-unification`
 - Start Date: 2024-09-11
 - RFC PR: [rust-lang/rfcs#3692](https://github.com/rust-lang/rfcs/pull/3692)
-- Rust Issue: [rust-lang/rust#3692](https://github.com/rust-lang/rust/issues/3692)
 
 # Summary
 [summary]: #summary