coin: Stop building Android vcpkg ports on non-Android hosts

RHEL 8.8, RHEL 8.10 and Windows 10_22H2 install vcpkg ports for the
Android ABIs, but none of them hosts a configuration that passes
-android-abis. The three templates that do, RHEL 9.6, macOS 15 arm and
Windows 11 24H2, install no Android ports at all. RHEL 8.8 is not
referenced by any platform configuration in the first place.

Nothing consumes the ports either way. No Android configuration sets
VCPKG_HOST_TRIPLET or VCPKG_TARGET_TRIPLET, so the vcpkg block in
qtbase's prepare_building_env.yaml has nothing to expand, and the
Android OpenSSL fallback in Qt6AndroidMacros.cmake looks for triplets
named arm64-android-dynamic, arm-neon-android-dynamic,
x64-android-dynamic and x86-android-dynamic, none of which is what gets
provisioned.

So this only removes provisioning time and image size. Drop the
ANDROID_NDK_HOME echo along with it, which was there for the Android
port build.

install-vcpkg-ports-android.sh and install-vcpkg-ports-android.ps1 are
left in place, unreferenced: RHEL 9.6 needs exactly the x86 and x86_64
pair the shell script installs, and Windows 11 24H2 the armeabi-v7a the
PowerShell one does, once the Android configurations name their
triplets.

Task-number: QTBUG-115715
Pick-to: 6.12
Change-Id: Ia48235058368bd8ffcfafe334a98326d8b608132
Reviewed-by: Elias Toivola <elias.toivola@qt.io>