Address review: revert contributing.md examples, remove unnecessary date-check comments

Author: santihdzs

src/contributing.md

@@ -444,20 +444,20 @@ Just a few things to keep in mind:
     For the action to pick the date, add a special annotation before specifying the date:
 
     ```md
-    <!-- date-check --> May 2026
+    <!-- date-check --> Nov 2025
     ```
 
     Example:
 
     ```md
-    As of <!-- date-check --> May 2026, the foo did the bar.
+    As of <!-- date-check --> Nov 2025, the foo did the bar.
     ```
 
     For cases where the date should not be part of the visible rendered output,
     use the following instead:
 
     ```md
-    <!-- date-check: May 2026 -->
+    <!-- date-check: Nov 2025 -->
     ```
 
   - A link to a relevant WG, tracking issue, `rustc` rustdoc page, or similar, that may provide

src/implementing-new-features.md

@@ -1,4 +1,3 @@
-<!-- date-check: May 2026 -->
 
 # Implementing new language features
 

src/normalization.md

@@ -164,7 +164,6 @@ In this example:
 
 When interfacing with the type system it will often be the case that it's necessary to request a type be normalized. There are a number of different entry points to the underlying normalization logic and each entry point should only be used in specific parts of the compiler.
 
-<!-- date-check: May 2026 -->
 An additional complication is that the compiler is currently undergoing a transition from the old trait solver to the new trait solver.
 As part of this transition our approach to normalization in the compiler has changed somewhat significantly, resulting in some normalization entry points being "old solver only" slated for removal in the long-term once the new solver has stabilized.
 The transition can be tracked via the [WG-trait-system-refactor](https://github.com/rust-lang/rust/labels/WG-trait-system-refactor) label in Github.

src/tests/minicore.md

@@ -1,6 +1,5 @@
 # `minicore` test auxiliary: using `core` stubs
 
-<!-- date-check: May 2026 -->
 
 [`tests/auxiliary/minicore.rs`][`minicore`] is a test auxiliary for ui/codegen/assembly/mir-opt test suites.
 It provides `core` stubs for tests that need to

src/tests/misc.md

@@ -2,7 +2,6 @@
 
 ## `RUSTC_BOOTSTRAP` and stability
 
-<!-- date-check: May 2026 -->
 
 This is a bootstrap/compiler implementation detail, but it can also be useful
 for testing: