Remove deprecated support for Alert.prompt with type as Callback

Summary:
This functionality was deprecated in [this commit](e2bd7db) on Feb 12th, 2019, originall in 0.59.0

Changelog:
[Breaking][General] Alert: Remove deprecated support for Alert.prompt with type as Callback (deprecated in 0.59)

Reviewed By: cpojer

Differential Revision: D19762618

fbshipit-source-id: a8edb6045bbc57d56e75fd281e602f5370ba1810

Author: elicwhite

Libraries/Alert/Alert.js

@@ -111,28 +111,6 @@ class Alert {
     keyboardType?: string,
   ): void {
     if (Platform.OS === 'ios') {
-      if (typeof type === 'function') {
-        console.warn(
-          'You passed a callback function as the "type" argument to Alert.prompt(). React Native is ' +
-            'assuming  you want to use the deprecated Alert.prompt(title, defaultValue, buttons, callback) ' +
-            'signature. The current signature is Alert.prompt(title, message, callbackOrButtons, type, defaultValue, ' +
-            'keyboardType) and the old syntax will be removed in a future version.',
-        );
-
-        const callback = type;
-        RCTAlertManager.alertWithArgs(
-          {
-            title: title || '',
-            type: 'plain-text',
-            defaultValue: message || '',
-          },
-          (id, value) => {
-            callback(value);
-          },
-        );
-        return;
-      }
-
       let callbacks = [];
       const buttons = [];
       let cancelButtonKey;