Revert "fpga manager: Adopted Authenticated BitStream loading support for Xilinx"

Revert "fpga manager: Adopted Authenticated BitStream loading support for Xilinx"

This reverts commit ed5a1413206f479a2ec68205539af4e299ce8ee7.

The FW (xilfpga) is using single pair of keys to authenticate the
Image. According to the xilinx flow we need to use a pair of
keys to provide the proper authentication support.
currently the FW don't have this support. So this patch
remove the Authenticated BitStream loading support.

Signed-off-by: Nava kishore Manne <navam@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>