lib/s3_req: remove v4 signature stub code
lib/s3_req: remove v4 signature stub code

b9e832dd0d5b2f6d8ca3bc634be2ccc8c92450cb accidentally added a stub
for v4 signature support. Remove it until the proper implementation
is done.

Signed-off-by: David Disseldorp <589a549dc9f982d9f46aeeb82a09ab6d87ccf1d8@suse.de>

ddiss/elasto,ddiss/elasto