chore: remove :block/title, :block/body and :block/unordered

For two reasons:

1. Reducing memory usage, both block/title and block/body are AST parsed
by Mldoc. After removing, logseq is able to handle 10k notes.

2. Simplify the db schema

src/main/frontend/handler/block.cljs

@@ -68,7 +68,7 @@
                (remove nil?)))))))
 
 ;; TODO: reduced version
-(defn walk-block
+(defn- walk-block
   [block check? transform]
   (let [result (atom nil)]
     (walk/postwalk