This commit is inspired by bytecodealliance#6480 and historical asks for Android
binaries. This does the bare minimum necessary to configure C compilers
such that we can produce binaries but I'll admit that I'm no Android
developer myself so I have no idea if these are actually suitable for
use anywhere. Otherwise though this build subsumes the preexisting check
in CI that the build works for Android, so that part is removed too.

This additionally changes how the NDK is managed from before. Previously
a GitHub Action was used to download Java and the NDK and additionally
used the `cargo ndk` subcommand. That's all removed now in favor of
configuring C compilers directly with a pre-installed version of the NDK
which should help reduce the CI dependencies a bit.