Remove unused gulp task remained from docusaurus 2 migration (#2308)

Summary:
**Summary**

Run yarn on the current master will produce an untracked file `website/static/css/Draft.css`. It's a remainder from the migration to Docusaurus 2 and should be deleted.

This will fix #2304

**Test Plan**

I ran `cd website && yarn && yarn start` and the doc website works fine locally.
Pull Request resolved: #2308

Reviewed By: claudiopro

Differential Revision: D19519361

Pulled By: mrkev

fbshipit-source-id: 7ea79dbfeb98f7dddba7d8fccc3cfc4708990788

gulpfile.js

@@ -38,7 +38,6 @@ var paths = {
     '!src/**/__mocks__/**/*.js',
   ],
   css: ['src/**/*.css'],
-  static: 'website/static',
 };
 
 var babelOptsJS = {
@@ -245,24 +244,6 @@ gulp.task(
   }),
 );
 
-gulp.task(
-  'website:static',
-  gulp.series(
-    'dist:min',
-    'css',
-    gulp.parallel(function() {
-      return gulp
-        .src(paths.dist + '/Draft.min.js')
-        .pipe(gulp.dest(paths.static + '/lib'));
-    }),
-    gulp.parallel(function() {
-      return gulp
-        .src(paths.dist + '/Draft.css')
-        .pipe(gulp.dest(paths.static + '/css'));
-    }),
-  ),
-);
-
 gulp.task(
   'check-dependencies',
   gulp.series(function() {
@@ -290,6 +271,6 @@ gulp.task(
     'check-dependencies',
     'clean',
     gulp.parallel('modules', 'flow'),
-    gulp.parallel('dist', 'dist:min', 'website:static'),
+    gulp.parallel('dist', 'dist:min'),
   ),
 );