Rely on native observe from LiveData instead of observe2 (DEV)

[mtwalli]

Replace observe2 with LiveDate.observe.
Since kotlin 1.4 it not necessarily to write the old syntax of observing LiveData in the Fragments or Activities.

old syntax: viewModel.liveData.observe(this, Observer { // TODO})

new syntax: viewModel.liveData.observe(this) {// TODO}

Therefore we don't have to write our own extension function to achieve that or use extension function from lifecycle library that was doing the same.

For more information please have a look at the following resources:
1- https://developer.android.com/jetpack/androidx/releases/lifecycle#2.3.0-beta01
2- https://android-review.googlesource.com/c/platform/frameworks/support/+/1413815

• UPDATE -
  I agreed with @d4rken to keep observe2 for Fragments as is

[d4rken]

Thanks for your PR @mtwalli .

While I like that the syntax is now nicer by default, I don't like that we would have to specify viewLifecycleOwner everywhere, how can we make this nicer?

[d4rken]

LGTM