Revert "Add prebuilt bootloader var and add bootloader to img zip"

Revert submission 1402265-cf-x86-bootloader

Reason for revert: Droidcop-triggered revert due to breakage https://android-build.googleplex.com/builds/quarterdeck?branch=git_master&target=adt3-userdebug&lkgb=6791187&lkbb=6791249&fkbb=6791216, bug 166380489
Reverted Changes:
Id67b7bddd:Add prebuilt bootloader var and add bootloader to ...
Id713eaf20:Added bootloader binary to cf x86 based targets

Change-Id: I89e95d4a6a0534c8217785be9b90632fa110bc41