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with NDK only up to r25, which includes an outdated embedded libc++.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/patches/qt/fix_android_jni_static.patch

@@ -1,17 +0,0 @@
---- old/qtbase/src/plugins/platforms/android/androidjnimain.cpp
-+++ new/qtbase/src/plugins/platforms/android/androidjnimain.cpp
-@@ -979,6 +979,14 @@ Q_DECL_EXPORT jint JNICALL JNI_OnLoad(JavaVM *vm, void */*reserved*/)
-         __android_log_print(ANDROID_LOG_FATAL, "Qt", "registerNatives failed");
-         return -1;
-     }
-+
-+    const jint ret = QT_PREPEND_NAMESPACE(QtAndroidPrivate::initJNI(vm, env));
-+    if (ret != 0)
-+    {
-+        __android_log_print(ANDROID_LOG_FATAL, "Qt", "initJNI failed");
-+        return ret;
-+    }
-+
-     QWindowSystemInterfacePrivate::TabletEvent::setPlatformSynthesizesMouse(false);
- 
-     m_javaVM = vm;