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

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with NDK only up to r25, which includes an outdated embedded libc++.

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

depends/packages/packages.mk

@@ -5,12 +5,10 @@ boost_packages = boost
 libevent_packages = libevent
 
 qrencode_linux_packages = qrencode
-qrencode_android_packages = qrencode
 qrencode_darwin_packages = qrencode
 qrencode_mingw32_packages = qrencode
 
 qt_linux_packages:=qt expat libxcb xcb_proto libXau xproto freetype fontconfig libxkbcommon libxcb_util libxcb_util_render libxcb_util_keysyms libxcb_util_image libxcb_util_wm
-qt_android_packages=qt
 qt_darwin_packages=qt
 qt_mingw32_packages=qt