Migrate upload of prebuilts for RISC-V

Re-work the prebuilt upload to AOSP to support RISC-V prebuilt uploads
from the new branch, remove any extraneous handling that was unused.

Bug: 338070272
Test: download_from_ci -u 11821503 -b 123456 (kernel_aarch64)
Test: download_from_ci -u 11790493 -b 123456 (kernel_riscv64)
Signed-off-by: Prashanth Swaminathan <prashanthsw@google.com>
Change-Id: I545c0c5ca5d546c22f4e6790891098fbe795f69e
1 file changed