Revert "Add docs_preprocessor crate to support Zed Docs" (#16880)

Temporarily revert #16700 to deal with this error:

`error: manifest path `../crates/docs_preprocessor/Cargo.toml` does not
exist` as it was causing the docs-preprocessor not to run, meaning
unexpanded templates were showing up in the public docs.

Reverts zed-industries/zed#16700

Release Notes:

- N/A

crates/docs_preprocessor/src/templates.rs

@@ -1,25 +0,0 @@
-use crate::PreprocessorContext;
-use regex::Regex;
-use std::collections::HashMap;
-
-mod action;
-mod keybinding;
-
-pub use action::*;
-pub use keybinding::*;
-
-pub trait Template {
-    fn key(&self) -> &'static str;
-    fn regex(&self) -> Regex;
-    fn parse_args(&self, args: &str) -> HashMap<String, String>;
-    fn render(&self, context: &PreprocessorContext, args: &HashMap<String, String>) -> String;
-
-    fn process(&self, context: &PreprocessorContext, content: &str) -> String {
-        self.regex()
-            .replace_all(content, |caps: &regex::Captures| {
-                let args = self.parse_args(&caps[1]);
-                self.render(context, &args)
-            })
-            .into_owned()
-    }
-}