[8.1] fix: remove ndjson.org (backport #5376) (#5391)

* fix: remove ndjson.org (#5376)

* fix: replace ndjson.org with ndjson spec

the original website expired and it's currently serving malicious content.

* Removing link

* capitalization fix

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Co-authored-by: nastasha.solomon <nastasha.solomon@elastic.co>
Co-authored-by: Joe Peeples <joe.peeples@elastic.co>
(cherry picked from commit 5beed29)

# Conflicts:
#	docs/serverless/investigate/timeline-templates-ui.mdx
#	docs/serverless/investigate/timelines-ui.mdx

* Delete docs/serverless directory and its contents

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Co-authored-by: kruskall <99559985+kruskall@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

docs/events/timeline-templates.asciidoc

@@ -131,8 +131,7 @@ NOTE: You cannot delete prebuilt templates.
 === Export and import Timeline templates
 
 You can import and export Timeline templates, which enables importing templates
-from one {kib} space or instance to another. Exported templates are saved in an
-http://ndjson.org[`ndjson`] file.
+from one {kib} space or instance to another. Exported templates are saved in an `ndjson` file.
 
 . Go to *Investigate* -> *Timelines* -> *Templates*.
 . To export templates, do one of the following:

docs/events/timeline-ui-overview.asciidoc

@@ -131,8 +131,7 @@ then select an action from the *Bulk actions* menu.
 == Export and import Timelines
 
 You can export and import Timelines, which enables you to share Timelines from one
-{kib} space or instance to another. Exported Timelines are saved as
-http://ndjson.org[`.ndjson`] files.
+{kib} space or instance to another. Exported Timelines are saved as `.ndjson` files.
 
 To export Timelines:
 

docs/getting-started/siem-ui.asciidoc

@@ -299,8 +299,7 @@ drop area for further introspection.
 ==== Export and import timelines
 
 You can import and export timelines, which enables importing timelines from one
-{kib} space or instance to another. Exported timelines are saved in an
-http://ndjson.org[`ndjson`] file.
+{kib} space or instance to another. Exported Timelines are saved in an `ndjson` file.
 
 . Go to *SIEM* -> *Timelines*.
 . To export timelines, do one of the following: