There are some untestable and unreachable code paths in the encoder
because it's not actually possible to fail to generate a genesis block.
The signature reports that it can return an error but has no cases where
it returns a non-nil error.  This CR simply removes that dead code.

Change-Id: I9559bf4a8f518ac3f97fb1256e9306e975ec1ce2
Signed-off-by: Jason Yellick <jyellick@us.ibm.com>