Doc Update: Remove INSTALL-Android since it's outdated (2 years)

There will be a FOSS Makefile for Android as soon as Monetas releases their client, according to FT:
"
[12:39] <fellowtraveler> All Monetas has is our own android makefile for OT, but it uses the latest open-source code
[12:40] <fellowtraveler> Monetas android client will be opensourced when released
"
Merge pull request #117 from lclc/rmAndroidDoc

Doc Update: Remove INSTALL-Android since it's outdated (2 years)