types: Use a React$ElementRef type for React.createRef type parameter.

As Greg pointed out it should be, a few months ago, after some
careful examination [1].

Since the `$FlowFixMe`s start getting flagged as "unused suppression
comments", remove them.

Strangely, `this.textInputRef.current` and friends are
`any(implicit)` after this. Hmm. Still, at least we can now say we're doing the
`React$ElementRef` part correctly.

[1] zulip#4278 (comment)

Author: chrisbobbe

src/common/InputWithClearButton.js

@@ -32,7 +32,7 @@ export default class InputWithClearButton extends PureComponent<Props, State> {
     canBeCleared: false,
     text: '',
   };
-  textInputRef = React.createRef<typeof TextInput>();
+  textInputRef = React.createRef<React$ElementRef<typeof TextInput>>();
 
   handleChangeText = (text: string) => {
     this.setState({
@@ -47,9 +47,6 @@ export default class InputWithClearButton extends PureComponent<Props, State> {
   handleClear = () => {
     this.handleChangeText('');
     if (this.textInputRef.current) {
-      // Should be fixed in RN v0.63 (#4245); see
-      // https://github.com/zulip/zulip-mobile/issues/4245#issuecomment-695104351.
-      // $FlowFixMe
       this.textInputRef.current.clear();
     }
   };

src/common/SmartUrlInput.js

@@ -69,15 +69,12 @@ export default class SmartUrlInput extends PureComponent<Props, State> {
   state = {
     value: '',
   };
-  textInputRef = React.createRef<typeof TextInput>();
+  textInputRef = React.createRef<React$ElementRef<typeof TextInput>>();
   unsubscribeFocusListener: () => void;
 
   componentDidMount() {
     this.unsubscribeFocusListener = this.props.navigation.addListener('focus', () => {
       if (this.textInputRef.current) {
-        // Should be fixed in RN v0.63 (#4245); see
-        // https://github.com/zulip/zulip-mobile/issues/4245#issuecomment-695104351.
-        // $FlowFixMe
         this.textInputRef.current.focus();
       }
     });
@@ -99,13 +96,9 @@ export default class SmartUrlInput extends PureComponent<Props, State> {
   urlPress = () => {
     const { textInputRef } = this;
     if (textInputRef.current) {
-      // Should be fixed in RN v0.63 (#4245); see
-      // https://github.com/zulip/zulip-mobile/issues/4245#issuecomment-695104351.
-      // $FlowFixMe
       textInputRef.current.blur();
       setTimeout(() => {
         if (textInputRef.current) {
-          // $FlowFixMe - same as above
           textInputRef.current.focus();
         }
       }, 100);

src/compose/ComposeBox.js

@@ -129,13 +129,13 @@ class ComposeBox extends PureComponent<Props, State> {
   static contextType = ThemeContext;
   context: ThemeData;
 
-  messageInputRef = React.createRef<typeof TextInput>();
-  topicInputRef = React.createRef<typeof TextInput>();
+  messageInputRef = React.createRef<React$ElementRef<typeof TextInput>>();
+  topicInputRef = React.createRef<React$ElementRef<typeof TextInput>>();
 
   // TODO: Type-check this, once we've adjusted our `react-redux`
   // wrapper to do the right thing. It should be
   //
-  //   mentionWarnings = React.createRef<typeof MentionWarnings>()
+  //   mentionWarnings = React.createRef<React$ElementRef<MentionWarnings>>()
   //
   // but we need our `react-redux` wrapper to be aware of
   // `{ forwardRef: true }`, since we use that.
@@ -348,9 +348,6 @@ class ComposeBox extends PureComponent<Props, State> {
     }
     completeEditMessage();
     if (this.messageInputRef.current !== null) {
-      // Should be fixed in RN v0.63 (#4245); see
-      // https://github.com/zulip/zulip-mobile/issues/4245#issuecomment-695104351.
-      // $FlowFixMe
       this.messageInputRef.current.blur();
     }
   };
@@ -365,9 +362,6 @@ class ComposeBox extends PureComponent<Props, State> {
       this.setMessageInputValue(message);
       this.setTopicInputValue(topic);
       if (this.messageInputRef.current !== null) {
-        // Should be fixed in RN v0.63 (#4245); see
-        // https://github.com/zulip/zulip-mobile/issues/4245#issuecomment-695104351.
-        // $FlowFixMe
         this.messageInputRef.current.focus();
       }
     }