Remove Blocks (#20138)

* Remove Blocks

* Remove Flight Server Runtime

There's no need for this now that the JSResource is part of the bundler
protocol. Might need something for Webpack plugin specifically later.

* Devtools

packages/react-devtools-shared/src/backend/DevToolsFiberComponentStack.js

@@ -35,7 +35,6 @@ function describeFiber(
     IndeterminateComponent,
     SimpleMemoComponent,
     ForwardRef,
-    Block,
     ClassComponent,
   } = workTagMap;
 
@@ -70,13 +69,6 @@ function describeFiber(
         owner,
         currentDispatcherRef,
       );
-    case Block:
-      return describeFunctionComponentFrame(
-        workInProgress.type._render,
-        source,
-        owner,
-        currentDispatcherRef,
-      );
     case ClassComponent:
       return describeClassComponentFrame(
         workInProgress.type,