Delete RCTBatchedBridge

Summary:
I've talked to several major community users, and they're all ok with deleting this
code.  There's several doc fixes which will make it easier for third
party developers which should land about the same time this will.

Also buried along with it is RCTJSCExecutor.

Reviewed By: javache

Differential Revision: D6880781

fbshipit-source-id: b4cb1143def6fd23a96290e478fa728adbedacd3

RNTester/RNTesterUnitTests/RCTAllocationTests.m

@@ -184,16 +184,16 @@ - (void)testUnderlyingBridgeIsDeallocated
   @autoreleasepool {
     bridge = [[RCTBridge alloc] initWithBundleURL:_bundleURL moduleProvider:nil launchOptions:nil];
     batchedBridge = bridge.batchedBridge;
-    XCTAssertTrue([batchedBridge isValid], @"RCTBatchedBridge should be valid");
+    XCTAssertTrue([batchedBridge isValid], @"RCTBridge impl should be valid");
     [bridge reload];
   }
 
   RCT_RUN_RUNLOOP_WHILE(batchedBridge != nil)
 
   XCTAssertNotNil(bridge, @"RCTBridge should not have been deallocated");
-  XCTAssertNil(batchedBridge, @"RCTBatchedBridge should have been deallocated");
+  XCTAssertNil(batchedBridge, @"RCTBridge impl should have been deallocated");
 
-  // Wait to complete the test until the new batchedbridge is also deallocated
+  // Wait to complete the test until the new bridge impl is also deallocated
   @autoreleasepool {
     batchedBridge = bridge.batchedBridge;
     [bridge invalidate];