[android] remove OfflineRegion.java, gitiginore and issue template. update README

.github/ISSUE_TEMPLATE/android.md

@@ -1,33 +0,0 @@
----
-name: Android
-about: Mapbox Maps SDK for Android
-
----
-<!--
-Hello and thanks for contributing to the Mapbox Maps SDK for Android! To help us diagnose your problem quickly, please:
-
- - Include a minimal demonstration of the bug, including code, logs, and screenshots.
- - Ensure you can reproduce the bug using the latest release.
- - Only post to report a bug or request a feature; direct all other questions to: https://stackoverflow.com/questions/tagged/mapbox
-
-Start with a brief description below this line. -->
-
-### Steps to reproduce
-
- 1.
- 2.
- 3.
-
-### Expected behavior
-
-
-
-### Actual behavior
-
-
-
-### Configuration
-
-**Android versions:** 
-**Device models:** 
-**Mapbox SDK versions:**