build, test, doc: Temporarily remove Android-related stuff

[hebasto]

Previously, our Android builds were geared towards generating APKs, which relied on Qt. However, after migrating to C++20, compiling for Android became unfeasible due to Qt 5.15's compatibility limitations with NDK only up to r25, which includes an outdated embedded libc++ (see #29360).

All removed stuff will be reinstated after migrating the build system to CMake and upgrading Qt to version 6.x.

This PR makes possible a clean migration to the CMake-based build system as it removes code, which is not used at this moment.

[DrahtBot]

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #29923 (depends: Remove Qt build-time dependencies by laanwj)
• #29868 (Reintroduce external signer support for Windows by hebasto)
• #29790 ([DO NOT MERGE] cmake: Migrate CI scripts to CMake-based build system -- WIP by hebasto)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

[theuni]

I guess the idea is that there's basically nothing worth salvaging from our current Android build procedure?

[maflcko]

if the images are re-added later, it should be done with a clean revert to avoid bloating the repo with identical-looking but binary-differing png blobs.

[hebasto]

I guess the idea is that there's basically nothing worth salvaging from our current Android build procedure?

The commit history keeps everything we might need when restoring Android builds.

[laanwj]

I guess the idea is that there's basically nothing worth salvaging from our current Android build procedure?

Not sure about that. i think the idea is that the current stuff is untestable in practice, which meant the CMake transition is blocked on it. E.g. porting it as-is wouldn't result in anything usable nor testable.

i've already cautioned not to go to wild with this and throw away android compatibility in the code, but removing the user facing build system support for now, seems fine with me.

[hebasto]

I guess the idea is that there's basically nothing worth salvaging from our current Android build procedure?

Not sure about that. i think the idea is that the current stuff is untestable in practice, which meant the CMake transition is blocked on it. E.g. porting it as-is wouldn't result in anything usable nor testable.

Exactly.

i've already cautioned not to go to wild with this and throw away android compatibility in the code, but removing the user facing build system support for now, seems fine with me.

I agree. No C++ source file is touched in this PR.