chore: remove obsolete content (#231)

Co-authored-by: Matteo Pace <[email protected]>

Author: theseion

content/3-about-rules/metadata.md

@@ -18,21 +18,6 @@ see a rule without a piece of metadata that you think is warranted
 please open either an [issue](https://github.com/coreruleset/coreruleset/issues) or a pull
 request.
 
-Tags about standards
---------------------
-
-We try our best to outline information about the vulnerability when each
-rule triggers. To that end we include metadata about where that
-vulnerability type can be found in various standards. These tags are
-currently prefixed with the standard type and will be capitalized. They
-will NOT start with OWASP_CRS. They consist of a the standard and then
-a slash to indicate the start of the data. The following standards are
-supported:
-
--   WASCTC
--   OWASP\_TOP\_10
--   PCI
-
 ### Tags about paranoia level
 
 Starting with version 3 we reintroduced the paranoia level concept.

content/4-about-plugins/_index.md

@@ -4,5 +4,3 @@ weight: 4
 pre: "<b>4. </b>"
 chapter: true
 ---
-
-# Development

content/6-development/_index.md

@@ -5,5 +5,3 @@ pre: "<b>6. </b>"
 chapter: true
 aliases: ["development"]
 ---
-
-# Operation