Nix refactor of Android SDK derivation

[jakubgs]

Refactoring Android SDK Nix derivation in preparation for a refactor of status-go derivations.

Since the SDK is used both in Android app build process and status-go build process I wanted to avoid importing it and passing it around via args explicitly. To do that I added our custom Android SDK+NDK to the pkgs which are passed around via callPackage implicitly.

I also did the same for xcodeWrapper by defining it as part of pkgs in nix/pkgs.nix.
And I removed some useless configuration for Buck which we don't use anymore.

And upgraded Nix from 2.3.2 to 2.3.4.

[status-github-bot]

Pull Request Checklist

• Docs: Updated the documentation, if affected
• Docs: Added or updated inline comments explaining intention of the code
• Tests: Ensured that all new UI elements have been assigned accessibility IDs
• Tests: Signaled need for E2E tests with label, if applicable
• Tests: Briefly described what was tested and what platforms were used
• UI: In case of UI changes, ensured that UI matches Figma
• UI: In case of UI changes, requested review from a Core UI designer
• UI: In case of UI changes, included screenshots of implementation

[status-im-auto]

Jenkins Builds

❔	Commit	#️⃣	Finished (UTC)	Duration	Platform	Result
✔️	3ee734f	#2	2020-04-23 16:24:47	~14 min	ios	📦ipa 📲
✔️	3ee734f	#2	2020-04-23 16:27:57	~18 min	android-e2e	📦apk 📲
✔️	3ee734f	#2	2020-04-23 16:29:20	~19 min	android	📦apk 📲
✔️	e61febc	#3	2020-04-24 07:57:03	~13 min	ios	📦ipa 📲
✔️	e61febc	#3	2020-04-24 07:58:06	~14 min	android-e2e	📦apk 📲
✔️	e61febc	#3	2020-04-24 07:58:08	~14 min	android	📦apk 📲

[Serhy]

@jakubgs Android builds gives me the crash right after app launch (confirmed with Android 8 real device and Android 10 (emulator) with this PR build and now with develop:

[jakubgs]

Damn.