Remove unnecessary access to UIKit on main thread in [RCTRedBox dealloc]

Summary:
Changelog: Fix main thread access to UIKit in RCTRedBox

{F611784226}

Xcode's main thread checker complains about this during reload. it is not needed to set `dataSource` and `delegate` to nil because the table view is about to be destroyed.

Reviewed By: mdvacca

Differential Revision: D28089039

fbshipit-source-id: 13b62cafb4790fc15b5a5dde131d4ae64bd97c82

React/CoreModules/RCTRedBox.mm

@@ -210,12 +210,6 @@
 
 RCT_NOT_IMPLEMENTED(-(instancetype)initWithCoder : (NSCoder *)aDecoder)
 
-- (void)dealloc
-{
-  _stackTraceTableView.dataSource = nil;
-  _stackTraceTableView.delegate = nil;
-}
-
 - (NSString *)stripAnsi:(NSString *)text
 {
   NSError *error = nil;