Recovery variants are built with -D__ANDROID_RECOVERY__

Recovery variant of a module is now by default built with
-D__ANDROID_RECOVERY__, thus eliminating the need to define a custom
macro to conditionally compile the module for the recovery mode.
(Of course, they can define their own macro if needed)

Bug: 63673171
Test: m -j
Change-Id: I1d1b990329793472b93c2f56080e72d690eef9ec