Remove unused rules for platform-robolectric-4.4-prebuilt

platform-robolectric-4.4-prebuilt was removed by
https://android-review.googlesource.com/c/platform/prebuilts/misc/+/2298317

,
and soong's special rules for platform-robolectric-4.4-prebuilt is not
needed anymore.

Test: m

Signed-off-by: utzcoz <utzcoz@gmail.com>
Change-Id: I3304aa1061d8b945b03cfe1a91f466ceb6ca1260