Revert "Move the Block helper type to its own file"

This fixes the broken tests

This reverts commit 286ae68fd6.

damus/Views/NoteContentView.swift

@@ -445,15 +445,7 @@ func render_blocks(blocks bs: Blocks, profiles: Profiles) -> NoteArtifactsSepara
     let blocks = bs.blocks
     
     let one_note_ref = blocks
-        .filter({
-            if case .mention(let mention) = $0,
-               case .note = mention.ref {
-                return true
-            }
-            else {
-                return false
-            }
-        })
+        .filter({ $0.is_note_mention })
         .count == 1
     
     var ind: Int = -1