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/settings/src/keymap_file.rs

@@ -22,34 +22,10 @@ pub struct KeymapBlock {
     bindings: BTreeMap<String, KeymapAction>,
 }
 
-impl KeymapBlock {
-    pub fn context(&self) -> Option<&str> {
-        self.context.as_deref()
-    }
-
-    pub fn bindings(&self) -> &BTreeMap<String, KeymapAction> {
-        &self.bindings
-    }
-}
-
 #[derive(Debug, Deserialize, Default, Clone)]
 #[serde(transparent)]
 pub struct KeymapAction(Value);
 
-impl ToString for KeymapAction {
-    fn to_string(&self) -> String {
-        match &self.0 {
-            Value::String(s) => s.clone(),
-            Value::Array(arr) => arr
-                .iter()
-                .map(|v| v.to_string())
-                .collect::<Vec<_>>()
-                .join(", "),
-            _ => self.0.to_string(),
-        }
-    }
-}
-
 impl JsonSchema for KeymapAction {
     fn schema_name() -> String {
         "KeymapAction".into()
@@ -159,10 +135,6 @@ impl KeymapFile {
 
         serde_json::to_value(root_schema).unwrap()
     }
-
-    pub fn blocks(&self) -> &[KeymapBlock] {
-        &self.0
-    }
 }
 
 fn no_action() -> Box<dyn gpui::Action> {