Merge bitcoin/bitcoin#30049: build, test, doc: Temporarily remove Android-related stuff

5deb0b024e build, test, doc: Temporarily remove Android-related stuff (Hennadii Stepanov)

Pull request description:

  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for Android became unfeasible due to Qt 5.15's compatibility limitations with NDK only up to r25, which includes an outdated embedded libc++ (see https://github.com/bitcoin/bitcoin/issues/29360).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.

ACKs for top commit:
  vasild:
    ACK 5deb0b024e
  fanquake:
    ACK 5deb0b024e - given none of this is currently tested/wont compile. Can be revisted in future.

Tree-SHA512: 3bc2ccfe881e11cc1d78c27acd6f1d86cfba86821ef3bb5eca2e80d978fdfa13659ec82284dcaadc507e2394524dea91d4b8f81d0030c1cef9708df8be76bf07

depends/hosts/android.mk

@@ -1,15 +0,0 @@
-ifeq ($(HOST),armv7a-linux-android)
-android_CXX=$(ANDROID_TOOLCHAIN_BIN)/$(HOST)eabi$(ANDROID_API_LEVEL)-clang++
-android_CC=$(ANDROID_TOOLCHAIN_BIN)/$(HOST)eabi$(ANDROID_API_LEVEL)-clang
-else
-android_CXX=$(ANDROID_TOOLCHAIN_BIN)/$(HOST)$(ANDROID_API_LEVEL)-clang++
-android_CC=$(ANDROID_TOOLCHAIN_BIN)/$(HOST)$(ANDROID_API_LEVEL)-clang
-endif
-
-android_CFLAGS=-std=$(C_STANDARD)
-android_CXXFLAGS=-std=$(CXX_STANDARD)
-
-android_AR=$(ANDROID_TOOLCHAIN_BIN)/llvm-ar
-android_RANLIB=$(ANDROID_TOOLCHAIN_BIN)/llvm-ranlib
-
-android_cmake_system=Android