docs: ReSTify table of contents in core.rst

Sphinx will now generate the table of contents automatically, which
avoids having the ToC getting out of sync with the rest of the document.
Signed-off-by: Josh Holland <anowlcalledjosh@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/security/keys/core.rst

@@ -16,17 +16,7 @@ The key service can be configured on by enabling:
 
 This document has the following sections:
 
-	- Key overview
-	- Key service overview
-	- Key access permissions
-	- SELinux support
-	- New procfs files
-	- Userspace system call interface
-	- Kernel services
-	- Notes on accessing payload contents
-	- Defining a key type
-	- Request-key callback service
-	- Garbage collection
+.. contents:: :local:
 
 
 Key Overview