Revert "fastboot: add preflash command to help with large downloads+flash"

This reverts commit 6f1cd0b2ad7a16d4ec0b5324f992cae33dc34f34.

It causes some devices to fail (b/9581613). Revert for now.

Change-Id: I076158c704c2b4f0459322aa157c19ebd0c4615f
2 files changed