Removing <TextInput>'s onTextInput event

Summary:
This is the first diff in the series. It removes Flow types for this feature to verify that we actually do not have any usages. After it lands, we will remove actual support on the native side.

There are several reasons why removing it is a good idea:
* There is no any evidence that this feature is actually useful. That was discussed several times (e.g. see T7936714) during RN lifetime and the overall consensus is: We need something else, something like sync `onChange` event instead of it.
* Supporting the previous point, it's not used (at least inside Facebook). I searched hard and I could find only one place where it's used: in the TextInput Example.
* To deliver more functionality we should lean towards W3C specs, this one is not W3C compliant.
* Supporting this Feature in Fabric is quite challenging, so I want to do it sooner than later.
* This feature was never documented.

Changelog: [Breaking] `<TextInput>::onTextInput` event was removed

Reviewed By: TheSavior

Differential Revision: D18456175

fbshipit-source-id: c7a8ed7a86b33ecc01d45497645fe249556fdf96

Libraries/Components/TextInput/TextInput.js

@@ -548,8 +548,6 @@ export type Props = $ReadOnly<{|
    */
   onContentSizeChange?: ?(e: ContentSizeChangeEvent) => mixed,
 
-  onTextInput?: ?(e: TextInputEvent) => mixed,
-
   /**
    * Callback that is called when text input ends.
    */
@@ -948,7 +946,6 @@ class InternalTextInput extends React.Component<Props> {
           onScroll={this._onScroll}
           onSelectionChange={this._onSelectionChange}
           onSelectionChangeShouldSetResponder={emptyFunctionThatReturnsTrue}
-          onTextInput={this._onTextInput}
           selection={selection}
           style={style}
           text={this._getText()}
@@ -983,7 +980,6 @@ class InternalTextInput extends React.Component<Props> {
           onFocus={this._onFocus}
           onScroll={this._onScroll}
           onSelectionChange={this._onSelectionChange}
-          onTextInput={this._onTextInput}
           selection={selection}
           style={style}
           text={this._getText()}
@@ -1111,10 +1107,6 @@ class InternalTextInput extends React.Component<Props> {
     }
   };
 
-  _onTextInput = (event: TextInputEvent) => {
-    this.props.onTextInput && this.props.onTextInput(event);
-  };
-
   _onScroll = (event: ScrollEvent) => {
     this.props.onScroll && this.props.onScroll(event);
   };