Delete BootPrebuilt.

They are unused.

Test: TH
Change-Id: I57c93ba93226b3694eba187a8531fbe00036d918
diff --git a/boot-userdebug.img b/boot-userdebug.img
deleted file mode 100644
index 4ed68f2..0000000
--- a/boot-userdebug.img
+++ /dev/null
Binary files differ