Convert android.test.legacy to Android.bp

The use of `TARGET_BUILD_PDK` has been deprecated in aosp/1320119, so
additional checks can be removed.

The license metadata on dependencies of module android.test.legacy has
been cleaned up in aosp/2995877. Therefore, the license of
android.test.legacy can be directly declared as "Android-Apache-2.0".

Bug: 319031379
Test: m android.test.legacy
Change-Id: I034ddd4f690205393c0d8ae385b8ad6bea7c4e6e