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/main.rs

@@ -1,58 +0,0 @@
-use anyhow::{Context, Result};
-use clap::{Arg, ArgMatches, Command};
-use docs_preprocessor::ZedDocsPreprocessor;
-use mdbook::preprocess::{CmdPreprocessor, Preprocessor};
-use std::io::{self, Read};
-use std::process;
-
-pub fn make_app() -> Command {
-    Command::new("zed-docs-preprocessor")
-        .about("Preprocesses Zed Docs content to provide rich action & keybinding support and more")
-        .subcommand(
-            Command::new("supports")
-                .arg(Arg::new("renderer").required(true))
-                .about("Check whether a renderer is supported by this preprocessor"),
-        )
-}
-
-fn main() -> Result<()> {
-    let matches = make_app().get_matches();
-
-    let preprocessor =
-        ZedDocsPreprocessor::new().context("Failed to create ZedDocsPreprocessor")?;
-
-    if let Some(sub_args) = matches.subcommand_matches("supports") {
-        handle_supports(&preprocessor, sub_args);
-    } else {
-        handle_preprocessing(&preprocessor)?;
-    }
-
-    Ok(())
-}
-
-fn handle_preprocessing(pre: &dyn Preprocessor) -> Result<()> {
-    let mut stdin = io::stdin();
-    let mut input = String::new();
-    stdin.read_to_string(&mut input)?;
-
-    let (ctx, book) = CmdPreprocessor::parse_input(input.as_bytes())?;
-
-    let processed_book = pre.run(&ctx, book)?;
-
-    serde_json::to_writer(io::stdout(), &processed_book)?;
-
-    Ok(())
-}
-
-fn handle_supports(pre: &dyn Preprocessor, sub_args: &ArgMatches) -> ! {
-    let renderer = sub_args
-        .get_one::<String>("renderer")
-        .expect("Required argument");
-    let supported = pre.supports_renderer(renderer);
-
-    if supported {
-        process::exit(0);
-    } else {
-        process::exit(1);
-    }
-}