Delete BootPrebuilt.

They are unused.

Test: TH
Change-Id: I2d7353374f8361c4e21a495ab0f0140dfb8c1deb
diff --git a/boot-userdebug.img b/boot-userdebug.img
deleted file mode 100644
index d0f92ac..0000000
--- a/boot-userdebug.img
+++ /dev/null
Binary files differ