Remove the last edited date from documentation pages (#11753)

I am bothered by the positioning of this immediately following the
content. I explored some other things, like forcing it the bottom of the
article, but in the end it was easiest to just hide it entirely

I think this belongs somewhere else, like in the footer — but I believe
that requires theme changes which are a bit more complicated than its
worth.
https://timvink.github.io/mkdocs-git-revision-date-localized-plugin/howto/override-a-theme/

The main goal here was SEO metadata anyway.

Originally added in #11164

Before

<img width="1334" alt="Screenshot 2025-02-24 at 12 57 56 PM"
src="https://github.com/user-attachments/assets/3f7423ff-fc18-40e8-be8a-f2e611af8221"
/>

Now, it's omitted.

Author: zanieb

docs/stylesheets/extra.css

@@ -214,11 +214,16 @@ h3.cli-reference {
   color: var(--md-accent-fg-color) !important;
 }
 
-
 /* Omit the first breadcrumb item, which is the "Introduction" */
 .md-path__list > .md-path__item:first-of-type {
   display: none;
 }
 .md-path__list > .md-path__item:nth-of-type(2):before {
   display: none;
 }
+
+/* Hide the modified date — its positioning is awkward but will require theme
+modifications */
+.md-source-file__fact {
+  visibility: hidden;
+}