Revert "Delete build-aml-prebuilts.sh"

Revert submission 1535006-bap

Reason for revert: Looks like it breaks the build as aapt2 depends on the build_number.txt this script was generating.  Error log below.
Reverted Changes:
I0f6b34310:Delete build-aml-prebuilts.sh
I4eae4153a:Replace use of build-aml-prebuilts

Change-Id: I7f5f1b3047f3d71eb8ac7bec95c5916425d5d8f2
FAILED: ninja: 'out/aml/soong/build_number.txt', needed by 'out/aml/soong/.intermediates/frameworks/base/tools/aapt2/aapt2/linux_glibc_x86_64/unstripped/aapt2', missing and no known rule to make it