Refine original Android sample

[zhouwg]

Purpose:

Thanks for original Android sample.
I met some issues when I learned original Android sample at the first time.

This PR is just refine original Android sample code so it's an Android turn-key example and more easily used in Android-based project(pre-study project).

How to practice/play with this PR:

adb logcat | grep WHISPER

Attention:
pls using debug version on real Android phone:

because there is a confirmed unknown bug(which was not brought by my codes) with release version in original Android sample

and I don't know why use complicated third-party binary Android framework in this Android sample.

I think "simple is beautiful" just like powerful whisper.cpp's implementation: Plain C/C++ implementation without dependencies .

so I will not spent extra time to fix bug in original Android sample.

[zhouwg]

I implemented a very concise implementation of Android example during my on-going PoC.

if it's considered well and accepted, I'll spent time to submit a new PR. so I'd like to close this PR accordingly.