Fix date on RFC 3243

Author: Manishearth

text/3243-packages-as-optional-namespaces.md

@@ -1,5 +1,5 @@
 - Feature Name: `packages_as_namespaces`
-- Start Date: (fill me in with today's date, 2022-03-09)
+- Start Date: 2022-03-09
 - RFC PR: [rust-lang/rfcs#3243](https://github.com/rust-lang/rfcs/pull/3243)
 - Rust Issue: [rust-lang/rust#122349](https://github.com/rust-lang/rust/issues/122349)