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with NDK only up to r25, which includes an outdated embedded libc++.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

@@ -38,11 +38,8 @@ Common `host-platform-triplet`s for cross compilation are:
 - `riscv32-linux-gnu` for Linux RISC-V 32 bit
 - `riscv64-linux-gnu` for Linux RISC-V 64 bit
 - `s390x-linux-gnu` for Linux S390X
-- `armv7a-linux-android` for Android ARM 32 bit
-- `aarch64-linux-android` for Android ARM 64 bit
-- `x86_64-linux-android` for Android x86 64 bit
 
-The paths are automatically configured and no other options are needed unless targeting [Android](../doc/build-android.md).
+The paths are automatically configured and no other options are needed.
 
 ### Install the required dependencies: Ubuntu & Debian