[monodroid] Do not build host or classic runtimes (#8256)

The `monodroid` build has been updated to only build the runtime files
that ship with .NET Android.

The generated `cmake-config.props` and `cmake-monodroid.targets` files
that determined which runtimes to build have had their content migrated
directly into `monodroid.targets`.  The corresponding generation logic
in `xaprepare` has been removed.

The `build-tools/scripts/build-monodroid` script and its dependencies
have been removed as they did not appear to be used anywhere.

`xabuild.csproj` will no longer be built as part of `make jenkins`.

Documentation/building/unix/dependencies.md

@@ -135,8 +135,7 @@ and to enable it again, issue the following command:
 
 ## macOS Dependencies
 
-The [`android-toolchain.projitems`](../../../build-tools/android-toolchain/android-toolchain.projitems), and
-[`monodroid.projitems`](../../../src/monodroid/monodroid.projitems) project files, among
+The [`android-toolchain.projitems`](../../../build-tools/android-toolchain/android-toolchain.projitems), among
 others, use the `@(RequiredProgram)` build action to check for the existence
 of a program within `$PATH` during the build. If a required program doesn't
 exist, then the build will fail and a suggested `brew install` command line

build-tools/scripts/BuildEverything.mk

@@ -29,4 +29,3 @@ leeroy: leeroy-all framework-assemblies
 leeroy-all:
 	$(call DOTNET_BINLOG,leeroy-all) $(SOLUTION) $(_MSBUILD_ARGS)
 	$(call DOTNET_BINLOG,setup-workload) -t:ConfigureLocalWorkload build-tools/create-packs/Microsoft.Android.Sdk.proj
-	$(call MSBUILD_BINLOG,leeroy-all,$(_SLN_BUILD)) /restore tools/xabuild/xabuild.csproj /p:Configuration=$(CONFIGURATION) $(_MSBUILD_ARGS)