Fixed double `onChange` event triggering from <TextInput> on iOS

Summary:
The problem was recently introduced in the last refactoring of the Text module.
There are two problem actually:
(1) Compare this current code with stable version.
In the stable version the event is only triggered here:
https://github.com/facebook/react-native/blob/0.52-stable/Libraries/Text/RCTTextField.m#L132-L140
In the new version the event is triggered in two places (which is obviously wrong).

(2) Executing `[_eventDispatcher sendTextEventWithType:RCTTextEventTypeChange:...]` and _onChange() actually do the same thing.
Historically, the single-line <TextInput> used the first approach and multi-line used second one. When we unify the logic, mixed both of them, which was apparenly wrong.
So, we have to remove another call of `[_eventDispatcher sendTextEventWithType:RCTTextEventTypeChange:...]`.
The the future we have to completly remove usage of `_eventDispatcher` from this component.

Depends on D6854770.

Reviewed By: fkgozali

Differential Revision: D6869678

fbshipit-source-id: 6705ee8dda2681ae184ef6716238cc8b62efeff1

Libraries/Text/TextInput/RCTBaseTextInputView.m

@@ -286,12 +286,6 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithFrame:(CGRect)frame)
     });
   }
 
-  [_eventDispatcher sendTextEventWithType:RCTTextEventTypeChange
-                                 reactTag:self.reactTag
-                                     text:backedTextInputView.attributedText.string
-                                      key:nil
-                               eventCount:_nativeEventCount];
-
   return YES;
 }
 
@@ -324,12 +318,6 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithFrame:(CGRect)frame)
        @"eventCount": @(_nativeEventCount),
     });
   }
-
-  [_eventDispatcher sendTextEventWithType:RCTTextEventTypeChange
-                                 reactTag:self.reactTag
-                                     text:backedTextInputView.attributedText.string
-                                      key:nil
-                               eventCount:_nativeEventCount];
 }
 
 - (void)textInputDidChangeSelection