flutter: update page; flutter-pub: add page (#10734)

* [flutter] added flutter-pub main commands

* Update flutter-pub.md

* Update flutter-pub.md

* Update flutter-pub.md

* Update pages/common/flutter-pub.md

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* Update pages/common/flutter-pub.md

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* Update pages/common/flutter-pub.md

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>

* Removing unnecessary commas

* Update pages/common/flutter-pub.md

Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

---------

Co-authored-by: K.B.Dharun Krishna <kbdharunkrishna@gmail.com>
Co-authored-by: Jack Lin <blueskyson1401@gmail.com>
Co-authored-by: Lena <126529524+acuteenvy@users.noreply.github.com>

pages/common/flutter.md

@@ -19,10 +19,6 @@
 
 `flutter run -d all`
 
-- Download all packages specified in `pubspec.yaml`:
-
-`flutter pub get`
-
 - Run tests in a terminal from the root of the project:
 
 `flutter test {{test/example_test.dart}}`