Use upstream corner radius

The history here is that the radius I'm removing was added in #884 after
having straight edges added in our custom fork for a while.

So, rather than override our override, I'm just reverting to the
upstream value, which is close in proximity, and closer to iMessages
radius.

// FREEBIE

Signal/src/view controllers/MessagesViewController.m

@@ -255,8 +255,6 @@ typedef enum : NSUInteger {
     sendLabel.font = [UIFont ows_regularFontWithSize:17.0f];
     sendLabel.textColor = [UIColor ows_materialBlueColor];
     sendLabel.textAlignment = NSTextAlignmentCenter;
-
-    self.inputToolbar.contentView.textView.layer.cornerRadius = 4.f;
 }
 
 - (void)viewWillAppear:(BOOL)animated {