[TIMOB-26239] Android: remove Ti.UI.currentWindow

[drauggres]

JIRA: https://jira.appcelerator.org/browse/TIMOB-26239

Ti.UI.currentWindow was deprecated and removed from other platforms long time ago, but is still present on Android (and cause memory leaks).

[build]

	Fails
🚫	Tests have failed, see below for more information.

	Messages
📖	👍 Hey!, You deleted more code than you added. That's awesome!
📖	💾 Here's the generated SDK zipfile.
📖	🎉 Another contribution from our awesome community member, drauggres! Thanks again for helping us make Titanium SDK better. 👍
📖	❌ 1 tests have failed There are 1 tests failing and 462 skipped out of 3633 total tests.

Tests:

Classname	Name	Time	Error
ios.Titanium.UI.NavigationWindow	#popToRootWindow	10.002	timeout of 10000ms exceeded

Generated by 🚫 dangerJS against a13e6e6

[garymathews]

CR: PASS

[keerthi1032]

FR Passed. Excueted TIMOB-4946 acceptance test which uses Ti.UI. current window getting undefined as expected.
Test Environment:
Name = Mac OS X
Version = 10.13.6
Architecture = 64bit
Cli =7.0.10
studio =5.1.2.201903111843
Node.js
Node.js Version = 8.12.0
npm Version = 6.4.1
Titanium CLI
CLI Version = 5.1.1
Titanium SDK
SDK Version = local 8.0.1.v20190321142528 and local master sdk 8.1.0.v20190321142031
Device =samsung s5 android 6
Emulator = PIXEL android8, nexus android 5
Target Platform = android