Add a deprecation note to the prolog rules in documentation

Mention that users should use submit-requirements instead of prolog
rules. Also remove links to the prolog documentation from the main index
page. This is how the warning message looks like
https://imgur.com/a/Ri6TP4d.

Release-Notes: Remove prolog rules doc page mention from the index page
Google-Bug-Id: b/246560406
Change-Id: I6f41355a7c12821380c53857c3801bc5a6895b4a

Documentation/index.txt

diff --git a/Documentation/index.txt b/Documentation/index.txt
index ee2c289..26e5350 100644
--- a/Documentation/index.txt
+++ b/Documentation/index.txt
@@ -51,9 +51,6 @@
 . Multi-project management
 .. link:user-submodules.html[Submodules]
 .. link:https://source.android.com/source/using-repo.html[Repo,role=external,window=_blank] (external)
-. Prolog rules
-.. link:prolog-cookbook.html[Prolog Cookbook]
-.. link:prolog-change-facts.html[Prolog Facts for Gerrit Changes]
 . link:intro-project-owner.html#project-deletion[Project deletion]
 
 == Customization and Integration

Documentation/prolog-cookbook.txt

diff --git a/Documentation/prolog-cookbook.txt b/Documentation/prolog-cookbook.txt
index c083f28..6c77109 100644
--- a/Documentation/prolog-cookbook.txt
+++ b/Documentation/prolog-cookbook.txt
@@ -1,5 +1,12 @@
 :linkattrs:
-= Gerrit Code Review - Prolog Submit Rules Cookbook
+= Gerrit Code Review - Prolog Submit Rules Cookbook (Deprecated)
+
+[WARNING]
+Prolog rules are no longer supported in Gerrit. Existing usages of prolog rules
+can be modified or deleted, but uploading new "rules.pl" files are rejected.
+Please use link:config-submit-requirements.html[submit requirements] instead.
+Note that the link:#SubmitType[Submit Type] being deprecated in this
+documentation page currently has no substitution in submit requirements.
 
 [[SubmitRule]]
 == Submit Rule