Revert "[Xamarin.Android.Build.Tasks] Fix Facade assembly deployment"

[jonpryor]

Reverts #337

Commit a7beb70 broke unit test execution. Jenkins build #190
ran 128 tests, while Jenkins build #191 executed 6.
Build #191 only contains two commits, and commit bf1bc93 --
PR #354 -- doesn't look like a plausible source of error.

The cause of the "broken unit test execution" is that the on-device
unit tests are exiting with an error:

Task "RunInstrumentationTests"
        ....
        INSTRUMENTATION_RESULT: shortMsg=android.runtime.JavaProxyThrowable
        INSTRUMENTATION_RESULT: longMsg=android.runtime.JavaProxyThrowable: System.IO.FileNotFoundException: Could not load file or assembly 'System.Runtime.Serialization, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e' or one of its dependencies.
...
xamarin-android/build-tools/scripts/UnitTestApks.targets:  warning : No `nunit2-results-path` bundle value found in command output! Cannot find NUnit2 XML output!

Commit a7beb70 stopped deploying facade assemblies, including
System.Runtime.Serialization, which is why it can't be found.

Revert commit a7beb70 so that on-device unit tests execute.